drm/radeon/kms: fix possible mis-detection of sideport on rs690/rs740

Check ulBootUpMemoryClock on AMD IGPs.

Fix regression noticed by Torsten Kaiser <just.for.lkml@googlemail.com>
Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_atombios.c

@@ -1029,8 +1029,15 @@ bool radeon_atombios_sideport_present(struct radeon_device *rdev)
 				      data_offset);
 		switch (crev) {
 		case 1:
+			/* AMD IGPS */
+			if ((rdev->family == CHIP_RS690) ||
+			    (rdev->family == CHIP_RS740)) {
+				if (igp_info->info.ulBootUpMemoryClock)
+					return true;
+			} else {
 				if (igp_info->info.ucMemoryType & 0xf0)
 					return true;
+			}
 			break;
 		case 2:
 			if (igp_info->info_2.ucMemoryType & 0x0f)