util: Move the m5ops.h file to a shared directory

util: Move the m5ops.h file to a shared directory

The header file m5ops.h contains a list of constants that should be
shared between the simulator and utilities. Move this header file to a
new top-level directory for shared files and rename constants to make
them suitable for inclusion in the main simulator.

The structure of the shared include directory is as follows:

include/gem5: Files that can be included from C code.
include/gem5/asm: Files that can be included from assembly code.
  asm/generic/: Files that aren't guest ISA specific
  asm/${isa}/: Files that are guest ISA specific

Change-Id: I1aa511057bcaa80cc2d566109ff26581558c4a41
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jose Marinho <jose.marinho@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/4261
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>