drm/radeon/dpm: implement vblank_too_short callback for cayman

Check if we can switch the mclk during the vblank time otherwise
we may get artifacts on the screen when the mclk changes.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_asic.c

@@ -1945,6 +1945,7 @@ static struct radeon_asic cayman_asic = {
 		.print_power_state = &ni_dpm_print_power_state,
 		.debugfs_print_current_performance_level = &ni_dpm_debugfs_print_current_performance_level,
 		.force_performance_level = &ni_dpm_force_performance_level,
+		.vblank_too_short = &ni_dpm_vblank_too_short,
 	},
 	.pflip = {
 		.pre_page_flip = &evergreen_pre_page_flip,