drm/amd/display: Clear the CUR_ENABLE register on DCN20 on DPP5

[Why]
On DCN20 & DCN30, the 6th DPP's & HUBP's are powered on permanently and
cannot be power gated. Thus, when dpp_reset() is invoked for the DPP5,
while it's still powered on, the cached cursor_state
(dpp_base->pos.cur0_ctl.bits.cur0_enable)
and the actual state (CUR0_ENABLE) bit are unsycned. This can cause a
double cursor in full screen with non-native scaling.

[How]
Force disable cursor on DPP5 on plane powerdown for ASICs w/ 6 DPPs/HUBPs.

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4673
Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Ivan Lipski <ivan.lipski@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 79b3c03)
Cc: stable@vger.kernel.org

Author: Ivan Lipski

drivers/gpu/drm/amd/display/dc/hwss/dcn20/dcn20_hwseq.c

@@ -614,6 +614,14 @@ void dcn20_dpp_pg_control(
 		 *		DOMAIN11_PGFSM_PWR_STATUS, pwr_status,
 		 * 		1, 1000);
 		 */
+
+		/* Force disable cursor on plane powerdown on DPP 5 using dpp_force_disable_cursor */
+		if (!power_on) {
+			struct dpp *dpp5 = hws->ctx->dc->res_pool->dpps[dpp_inst];
+			if (dpp5 && dpp5->funcs->dpp_force_disable_cursor)
+				dpp5->funcs->dpp_force_disable_cursor(dpp5);
+		}
+
 		break;
 	default:
 		BREAK_TO_DEBUGGER();