base: Add operators to SatCounter

base: Add operators to SatCounter

Add shift, add and subtract assignment operators, as well as
copy and move constructor and assignments to SatCounter, so
that it they can be used by the prefetchers.

Also add extra useful functions to calculate saturation
oercentile so that the instantiator does not need to be aware
of the counter's maximum value.

Change-Id: I61d0cb28c8375b9d2774a39011e4a0aa6fe9ccb7
Signed-off-by: Daniel <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17996
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>