x86: Split apart x87's FSW and TOP, and add a missing break.

The FSW and TOP values are technically part of the same register, but
they have very different behaviors. One of them can be renamed and
float along without affecting global state, while the other requires
serialization. They just need to *look* like the same register when
read by the user.

Also, there was a missing break in setMiscRegNoEffect.

Change-Id: If58de0f566f65068208240f4001209fb9e1826d6
Reviewed-on: https://gem5-review.googlesource.com/6441
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>

x86: Adjust the size of the values written to the x87 misc registers
All x87 misc registers are implemented in an array of 64 bit values
but in real hardware the size of some of these registers is smaller.
Previsouly all 64 bits where incorrectly set and then later read. To
ensure correctness we mask the value in setMiscRegNoEffect to write
only the valid bits.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>

x86: Add support for FLDENV & FNSTENV

copyright: Change HP copyright on x86 code to be more friendly

X86: Put in stubs for x87, 64 bit and 128 bit SIMD instruction microcode.