drm/amd/display: Fix idle check for shared firmware state

[WHY]
We still had an instance of get_idle_state checking the PMFW scratch
register instead of the actual idle allow signal.

[HOW]
Replace it with the SW state check for whether we had allowed idle
through notify_idle.

Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: Duncan Ma <duncan.ma@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc.c

@@ -4847,22 +4847,16 @@ void dc_exit_ips_for_hw_access(struct dc *dc)
 
 bool dc_dmub_is_ips_idle_state(struct dc *dc)
 {
-	uint32_t idle_state = 0;
-
 	if (dc->debug.disable_idle_power_optimizations)
 		return false;
 
 	if (!dc->caps.ips_support || (dc->config.disable_ips == DMUB_IPS_DISABLE_ALL))
 		return false;
 
-	if (dc->hwss.get_idle_state)
-		idle_state = dc->hwss.get_idle_state(dc);
-
-	if (!(idle_state & DMUB_IPS1_ALLOW_MASK) ||
-		!(idle_state & DMUB_IPS2_ALLOW_MASK))
-		return true;
+	if (!dc->ctx->dmub_srv)
+		return false;
 
-	return false;
+	return dc->ctx->dmub_srv->idle_allowed;
 }
 
 /* set min and max memory clock to lowest and highest DPM level, respectively */