base: Move SatCounter to base directory

base: Move SatCounter to base directory

Saturating counters are used by many objects, not only
the cpu predictors. Therefore, move the class to the
base folder so that it can be more easily used.

Change-Id: I26f799324bdd8720ab8834c72a2002149cee777c
Signed-off-by: Daniel <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17993
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>