mem-cache: Fix FALRU inCachesMask initialization

mem-cache: Fix FALRU inCachesMask initialization

inCachesMask is not being initialized, which triggers an assertion
on insertion. Fix this by implementing a default constructor for
the FALRUBlk.

Change-Id: I587cf5e0191c4587d938e6ab6036ec1b32f37793
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/13207
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>