Clean up GPUVM aperture management

Non-canonical GPUVM aperture doesn't exist on dGPUs. Remove comments
and code that say otherwise.

Fix alignment of GPUVM aperture for gfx801. Requires the same workaround
as gfx802. It's not used for anything on gfx801 yet, but will be soon.

Change-Id: I88607fe7b340081cc0715b85f28fdbf5f1bb0ad7


[ROCm/ROCR-Runtime commit: b837c3e7b0]

projects/rocr-runtime/src/memory.c

@@ -294,6 +294,12 @@ hsaKmtUnmapMemoryToGPU(
 {
 	CHECK_KFD_OPEN();
 
+	if (MemoryAddress == NULL) {
+		/* Workaround for runtime bug */
+		fprintf(stderr, "FIXME: Unmapping NULL pointer\n");
+		return HSAKMT_STATUS_SUCCESS;
+	}
+
 	if (!fmm_unmap_from_gpu(MemoryAddress))
 		return HSAKMT_STATUS_SUCCESS;
 	else