mem-cache: Forward declare ReplaceableEntry

Forward declare ReplaceableEntry where in classes where pointers
to it are used.

Change-Id: I49c08d36442a563d7a6b4c9bcd7eba3591d29b60
Reviewed-on: https://gem5-review.googlesource.com/11096
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

src/mem/cache/tags/base.hh

@@ -63,6 +63,7 @@
 #include "sim/clocked_object.hh"
 
 class BaseCache;
+class ReplaceableEntry;
 
 /**
  * A common base class of Cache tagstore objects.

src/mem/cache/tags/fa_lru.hh

@@ -68,6 +68,8 @@
 // TrackedCaches class
 //#define FALRU_DEBUG
 
+class ReplaceableEntry;
+
 // A bitmask of the caches we are keeping track of. Currently the
 // lowest bit is the smallest cache we are tracking, as it is
 // specified by the corresponding parameter. The rest of the bits are

src/mem/cache/tags/sector_tags.hh

@@ -45,6 +45,7 @@
 #include "params/SectorTags.hh"
 
 class BaseReplacementPolicy;
+class ReplaceableEntry;
 
 /**
  * A SectorTags cache tag store.