drm/amd/display: Allow PSTATE chnage when no displays are enabled

[Why]
When no displays are currently enabled, display driver should not
disallow PSTATE switching.

[How]
Allow PSTATE switching if either the active configuration supports it,
or there are no active displays.
Tested-by: NDaniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: NAric Cyr <aric.cyr@amd.com>
Reviewed-by: NJun Lei <Jun.Lei@amd.com>
Acked-by: NAnson Jacob <anson.jacob@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/clk_mgr/dcn30/dcn30_clk_mgr.c

@@ -251,6 +251,7 @@ static void dcn3_update_clocks(struct clk_mgr *clk_mgr_base,
 	struct dmcu *dmcu = clk_mgr_base->ctx->dc->res_pool->dmcu;
 	bool force_reset = false;
 	bool update_uclk = false;
+	bool p_state_change_support;
 
 	if (dc->work_arounds.skip_clock_update || !clk_mgr->smu_present)
 		return;
@@ -291,8 +292,9 @@ static void dcn3_update_clocks(struct clk_mgr *clk_mgr_base,
 		clk_mgr_base->clks.socclk_khz = new_clocks->socclk_khz;
 
 	clk_mgr_base->clks.prev_p_state_change_support = clk_mgr_base->clks.p_state_change_support;
-	if (should_update_pstate_support(safe_to_lower, new_clocks->p_state_change_support, clk_mgr_base->clks.p_state_change_support)) {
-		clk_mgr_base->clks.p_state_change_support = new_clocks->p_state_change_support;
+	p_state_change_support = new_clocks->p_state_change_support || (display_count == 0);
+	if (should_update_pstate_support(safe_to_lower, p_state_change_support, clk_mgr_base->clks.p_state_change_support)) {
+		clk_mgr_base->clks.p_state_change_support = p_state_change_support;
 
 		/* to disable P-State switching, set UCLK min = max */
 		if (!clk_mgr_base->clks.p_state_change_support)