util: Move m5op.h to the shared include directory

util: Move m5op.h to the shared include directory

The header file with C declarations for m5ops is sometimes needed by
code outside of the util/m5 directory. Move this file to the shared
include directory and factor out flags to a generic asm header. Note
that applications that need to call m5ops still need to link with
libm5.a or implement their own trampolines.

Change-Id: I36a3f459ed71593e38b869dc2b1302c810f92276
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jose Marinho <jose.marinho@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/4265
Reviewed-by: Gabe Black <gabeblack@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>