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/gpu-compute/fetch_unit.cc

@@ -145,7 +145,7 @@ FetchUnit::initiateFetch(Wavefront *wavefront)
     }
 
     // set up virtual request
-    Request *req = new Request(0, vaddr, size, Request::INST_FETCH,
+    RequestPtr req = new Request(0, vaddr, size, Request::INST_FETCH,
                                computeUnit->masterId(), 0, 0, 0);
 
     PacketPtr pkt = new Packet(req, MemCmd::ReadReq);