mem: Add system request flag for dGPUs

dGPUs can translate a virtual address and will not know if the address
resides in system/host memory or device/dGPU memory until the
translation is complete. In order to mark requests as going to either
system memory or device memory we add a field to the Request class.

Change-Id: Ib1e80e8d03ecdfeb11c24d979ccc4b912ce07f91
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/51852
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>

src/mem/request.hh

@@ -436,6 +436,12 @@ class Request
      */
     uint32_t _substreamId = 0;
 
+    /**
+     * For fullsystem GPU simulation, this determines if a requests
+     * destination is system (host) memory or dGPU (device) memory.
+     */
+    bool _systemReq = 0;
+
     /** The virtual address of the request. */
     Addr _vaddr = MaxAddr;
 
@@ -862,6 +868,10 @@ class Request
         return _contextId;
     }
 
+    /* For GPU fullsystem mark this request is not to device memory. */
+    void setSystemReq(bool sysReq) { _systemReq = sysReq; }
+    bool systemReq() const { return _systemReq; }
+
     bool
     hasStreamId() const
     {