misc: Substitute pointer to Request with aliased RequestPtr

Every usage of Request* in the code has been replaced with the
RequestPtr alias.  This is a preparing patch for when RequestPtr will be
the typdefed to a smart pointer to Request rather then a raw pointer to
Request.

Change-Id: I73cbaf2d96ea9313a590cdc731a25662950cd51a
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/10995
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>

src/mem/cache/cache.cc

@@ -872,7 +872,8 @@ Cache::cleanEvictBlk(CacheBlk *blk)
     assert(!writebackClean);
     assert(blk && blk->isValid() && !blk->isDirty());
     // Creating a zero sized write, a message to the snoop filter
-    Request *req =
+
+    RequestPtr req =
         new Request(regenerateBlkAddr(blk), blkSize, 0,
                     Request::wbMasterId);
     if (blk->isSecure())