drm/amdgpu/gfx8: update PA_SC_RASTER_CONFIG:PKR_MAP only

BugLink: http://bugs.launchpad.net/bugs/1546572

Use default value as a base.
Signed-off-by: Flora Cui <Flora.Cui@amd.com>
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>
(cherry picked from commit c27816a8)
Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/gpu/drm/amd/amdgpu/gfx_v8_0.c

@@ -3125,7 +3125,7 @@ static void gfx_v8_0_setup_rb(struct amdgpu_device *adev,
 	mutex_lock(&adev->grbm_idx_mutex);
 	for (i = 0; i < se_num; i++) {
 		gfx_v8_0_select_se_sh(adev, i, 0xffffffff);
-		data = 0;
+		data = RREG32(mmPA_SC_RASTER_CONFIG);
 		for (j = 0; j < sh_per_se; j++) {
 			switch (enabled_rbs & 3) {
 			case 0: