util, m5: Use consistent naming for m5op C symbols

util, m5: Use consistent naming for m5op C symbols

Rename m5op C symbols to be prefixed all lower case, separated by
underscore, and prefixed by m5. This avoids potential name clashes for
short names such as arm.

Change-Id: Ic42f94d8a722661ef96c151d627e31eeb2e51490
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jose Marinho <jose.marinho@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/4264
Reviewed-by: Gabe Black <gabeblack@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>