drm/amd/display: fix register write sequence for LINK_SQUARE_PATTERN

[why&how]
write LINK_SQUARE_PATTERN_num + 1 for square pulse pattern.
Specs requirement to write this register prior to write LINK_QUAL_LANEX_SET.

Acked-by: Aurabindo Pillai <[e-mail]>
Signed-off-by: Wenjing Liu <[e-mail]>
Reviewed-by: George Shen <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

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

···
 			return false;
 
 		if (link->dpcd_caps.dpcd_rev.raw >= DPCD_REV_12) {
+#if defined(CONFIG_DRM_AMD_DC_DCN)
+			if (test_pattern == DP_TEST_PATTERN_SQUARE_PULSE)
+				core_link_write_dpcd(link,
+						DP_LINK_SQUARE_PATTERN,
+						p_custom_pattern,
+						1);
+
+#endif
 			/* tell receiver that we are sending qualification
 			 * pattern DP 1.2 or later - DP receiver's link quality
 			 * pattern is set using DPCD LINK_QUAL_LANEx_SET

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

···
 #ifndef DP_DFP_CAPABILITY_EXTENSION_SUPPORT
 #define DP_DFP_CAPABILITY_EXTENSION_SUPPORT		0x0A3
 #endif
+#ifndef DP_LINK_SQUARE_PATTERN
+#define DP_LINK_SQUARE_PATTERN				0x10F
+#endif
 #ifndef DP_DSC_CONFIGURATION
 #define DP_DSC_CONFIGURATION				0x161
 #endif