mem-cache: adding late prefetch stats

Adding a late prefetch stat plus stats for each reason a prefetch can be
detected as late

Change-Id: Ia6d5294e8ce58b2b0aae2be98fd0cee83be73b8d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/47204
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Daniel Carvalho <odanrc@yahoo.com.br>
Tested-by: kokoro <noreply+kokoro@google.com>
3 files changed