drm/amd/display: Reduce SubVP + DRR stretch margin

[Description]
- Having excessively large margin causes failure in the static
schedulability check in some cases for SubVP + DRR
- 100us of DRR margin is sufficient based on a weeks worth of
stress testing on different display configs

Reviewed-by: Michael Strauss <[e-mail]>
Acked-by: Qingqing Zhuo <[e-mail]>
Signed-off-by: Alvin Lee <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/dc/dc_stream.h

···
 	unsigned int cust_pattern_size;
 };
 
-#define SUBVP_DRR_MARGIN_US 600 // 600us for DRR margin (SubVP + DRR)
+#define SUBVP_DRR_MARGIN_US 100 // 100us for DRR margin (SubVP + DRR)
 
 enum mall_stream_type {
 	SUBVP_NONE, // subvp not in use