drm/amd/display: Allow bandwidth validation for 0 streams.

[Why]
Bandwidth calculations are triggered for non zero streams, and
in case of 0 streams, these calculations were skipped with
pstate status not being updated.

[How]
As the pstate status is applicable for non zero streams, check
added for allowing 0 streams inline with dcn internal bandwidth
validations.
Signed-off-by: Bindu Ramamurthy <bindu.r@amd.com>
Reviewed-by: Roman Li <Roman.Li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c

@@ -3236,7 +3236,7 @@ static noinline bool dcn20_validate_bandwidth_fp(struct dc *dc,
 	voltage_supported = dcn20_validate_bandwidth_internal(dc, context, false);
 	dummy_pstate_supported = context->bw_ctx.bw.dcn.clk.p_state_change_support;
 
-	if (voltage_supported && dummy_pstate_supported) {
+	if (voltage_supported && (dummy_pstate_supported || !(context->stream_count))) {
 		context->bw_ctx.bw.dcn.clk.p_state_change_support = false;
 		goto restore_dml_state;
 	}