drm/amd/display: Add DML2 folder to include path

Add DML2 compilation rule in the Makefile.
Reviewed-by: Chaitanya Dhere <chaitanya.dhere@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@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/dml2/Makefile

@@ -67,6 +67,7 @@ frame_warn_flag := -Wframe-larger-than=2048
 endif
 endif
 
+subdir-ccflags-y += -I$(FULL_AMD_DISPLAY_PATH)/dc/dml2
 CFLAGS_$(AMDDALPATH)/dc/dml2/display_mode_core.o := $(dml2_ccflags) $(frame_warn_flag)
 CFLAGS_$(AMDDALPATH)/dc/dml2/display_mode_util.o := $(dml2_ccflags)
 CFLAGS_$(AMDDALPATH)/dc/dml2/dml2_wrapper.o := $(dml2_ccflags)