drm/amd/display: Force prefetch mode to 0

[Why]
On APU should be always using prefetch mode 0.
Currently, sometimes prefetch mode 1 is being
used causing system to hard hang due to
minTTUVBlank being too low.

[How]
Any ASIC running DCN21 will by default allow
self refresh and mclk switch. This sets both
min and max prefetch mode to 0 by default.
Signed-off-by: Isabel Zhang <isabel.zhang@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn21/dcn21_resource.c

@@ -301,7 +301,9 @@ struct _vcs_dpi_soc_bounding_box_st dcn2_1_soc = {
 	.xfc_bus_transport_time_us = 4,
 	.xfc_xbuf_latency_tolerance_us = 4,
 	.use_urgent_burst_bw = 1,
-	.num_states = 8
+	.num_states = 8,
+	.allow_dram_self_refresh_or_dram_clock_change_in_vblank
+			= dm_allow_self_refresh_and_mclk_switch
 };
 
 #ifndef MAX