mem-cache: Signature Path Prefetcher

Related paper:
Lookahead Prefetching with Signature Path
J Kim, PV Gratz, ALN Reddy
The 2nd Data Prefetching Championship (DPC2), 2015

Change-Id: I2319be2fa409f955f65e1bf1e1bb2d6d9a4fea11
Reviewed-on: https://gem5-review.googlesource.com/c/14737
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>