drm/amdgpu: add asic callback to get memsize register

Newer asics use different registers so abstract it.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index a702472..c0d12e8 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -713,7 +713,7 @@
 		return true;
 	}
 	/* then check MEM_SIZE, in case the crtcs are off */
-	reg = RREG32(mmCONFIG_MEMSIZE);
+	reg = amdgpu_asic_get_config_memsize(adev);
 
 	if (reg)
 		return false;