style: change C/C++ source permissions to noexec

Several files in the repository were tracked with execute permissions
even though the files are just normal C/C++ files (and the one .isa).

Change-Id: I976b096acab4a1fc74c5699ef1f9b222c1e635c2
Reviewed-on: https://gem5-review.googlesource.com/7241
Reviewed-by: Gabe Black <gabeblack@google.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

MIPS: Use BitUnions instead of bits() functions and constants.
Also fix style issues in regions around these changes.

go back and fix up MIPS copyright headers

fix MIPS headers

Add in files from merge-bare-iron, get them compiling in FS and SE mode

mips import pt. 1

src/arch/mips/SConscript:
"mips import pt.1".