util: c++-ify the call type in the m5 utility.

util: c++-ify the call type in the m5 utility.

Use a class to track call type information, and mostly avoid having to
use ifdefs to include or not include support for individual call types.

Change-Id: I731c99e67ea1c511d53431df3f77b4a959919a59
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27549
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabeblack@google.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Gabe Black <gabeblack@google.com>