drm/radeon: disable dpm on rv770 by default

There seem to be stability issues on a number of cards.

bugs:
https://bugs.freedesktop.org/show_bug.cgi?id=76286
https://bugzilla.redhat.com/show_bug.cgi?id=1085785
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=741619

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: matthias.graf@st.ovqu.de
Cc: bp@alien8.de
Cc: stable@vger.kernel.org

drivers/gpu/drm/radeon/radeon_pm.c

@@ -1257,6 +1257,7 @@ int radeon_pm_init(struct radeon_device *rdev)
 	case CHIP_RV670:
 	case CHIP_RS780:
 	case CHIP_RS880:
+	case CHIP_RV770:
 	case CHIP_BARTS:
 	case CHIP_TURKS:
 	case CHIP_CAICOS:
@@ -1273,7 +1274,6 @@ int radeon_pm_init(struct radeon_device *rdev)
 		else
 			rdev->pm.pm_method = PM_METHOD_PROFILE;
 		break;
-	case CHIP_RV770:
 	case CHIP_RV730:
 	case CHIP_RV710:
 	case CHIP_RV740: