arm: update hint instruction decoding to match ARMv8.5

This fixes:

- unallocated hints that have since been allocated
- unallocated and unimplemented hint instructions being treated as
Unknown instead of the correct NOP
- missing encoding for DBG on A32

Unallocated and unimplemented hints give a warning if executed.

The most important fix was for the CSDB Spectre mitigation
instruction, which was added recently and previously unallocated and
treated as Unknown.

The Linux kernel v4.18 ARMv7 uses CSDB it and boot would
fail with "undefined instruction" since Linux commit
1d4238c56f9816ce0f9c8dbe42d7f2ad81cb6613

Change-Id: I283da3f08a9af4148edc6fb3ca2930cbb97126b8
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/13475
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

arch-arm: Corrected encoding for T32 HVC instruction

This patch corrects the encoding of the HVC (Hypervisor Call) for the
T32 instruction set.

Change-Id: I6f77eaf5c586697e9ccd588419c61e6d90c6c7bf
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Chuan Zhu <chuan.zhu@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5541
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

arm: Add support for ARMv8 (AArch64 & AArch32)

Note: AArch64 and AArch32 interworking is not supported. If you use an AArch64
kernel you are restricted to AArch64 user-mode binaries. This will be addressed
in a later patch.

Note: Virtualization is only supported in AArch32 mode. This will also be fixed
in a later patch.

Contributors:
Giacomo Gabrielli (TrustZone, LPAE, system-level AArch64, AArch64 NEON, validation)
Thomas Grocutt (AArch32 Virtualization, AArch64 FP, validation)
Mbou Eyole (AArch64 NEON, validation)
Ali Saidi (AArch64 Linux support, code integration, validation)
Edmund Grimley-Evans (AArch64 FP)
William Wang (AArch64 Linux support)
Rene De Jong (AArch64 Linux support, performance opt.)
Matt Horsnell (AArch64 MP, validation)
Matt Evans (device models, code integration, validation)
Chris Adeniyi-Jones (AArch64 syscall-emulation)
Prakash Ramrakhyani (validation)
Dam Sunwoo (validation)
Chander Sudanthi (validation)
Stephan Diestelhorst (validation)
Andreas Hansson (code integration, performance opt.)
Eric Van Hensbergen (performance opt.)
Gabe Black

ARM: Clean up condCodes in IT blocks.

ARM: Implement DBG instruction that doesn't do much for now.

ARM: Implement DSB, DMB, ISB

ARM: Implement CLREX

ARM: BX instruction can be contitional if last instruction in a IT block

Branches are allowed to be the last instuction in an IT block. Before it was
assumed that they could not. So Branches in thumb2 were Uncond.

ARM: Hook the misc instructions into the thumb decoder.

ARM: BXJ should be BX when there is no J support

ARM: Decode the CPS instruction.

ARM: Make sure some undefined thumb32 instructions fault.

ARM: Decode the enterx and leavex instructions.

ARM: When an instruction is intentionally undefined, fault on it.

ARM: Decode the clz instruction.

ARM: Decode the nop instruction.

ARM: Decode MRS and MSR for thumb.

ARM: Hook SVC into the thumb decoder.

ARM: Add support for "SUBS PC, LR and related instructions".

ARM: Hook the new branch instructions into the 32 bit thumb decoder.

ARM: Hook the new branch instructions into the 16 bit thumb decoder.

ARM: Eliminate the old style branch instructions.

ARM: Hook the new branch instructions into the ARM decoder.

ARM: Get rid of the unused Jump format.

ARM: Split the condition codes out of the CPSR.

This allows those bits to be renamed while allowing the other fields to
control the behavior of the processor.

ARM: Link register is trashed by non-executed branch and link operations.

ARM: Simplify the ISA desc by pulling some classes out of it.

ARM: Make the isa parser aware that CPSR is being used.

ARM: Pull some static code out of the isa desc and create miscregs.hh.

arm: add ARM support to M5