drm/amd/display: Properly guard display_mode_vba with DCN2

[Why]

display_mode_vba is for DCN2 and up. When building for upstream (DCN1
enabled only), there will be a build error, since display_mode_vba.c/h
is stripped out.

Note that building DCN1 only with internal dal-dev is still fine, since
display_mode_vba.h is not stripped out internally - only in upstream.
The make directives therefore stll work, and so will any #include's.

[How]

Since subsequent generations require DCN2 enabled anyways, guard the
makefile directive for display_mode_vba.o with DCN2. Guard any includes
with DCN2. In addition, guard the entire contents of display_mode_vba.h
with DCN2, to simulate the file being stripped out in upstream.

A forward declaration for 'struct display_mode_lib' also needs to be
added in display_mode_lib.h. Previously, display_mode_vba.h contained
the forward declaration, and display_mode_lib.h in turn included it.
This won't work if mode_vba.h is stripped out, requring mode_lib.h to do
so itself.
Signed-off-by: Leo Li <sunpeng.li@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dml/Makefile

@@ -33,8 +33,9 @@ endif
 dml_ccflags := -mhard-float -msse $(cc_stack_align)
 
 CFLAGS_display_mode_lib.o := $(dml_ccflags)
-CFLAGS_display_mode_vba.o := $(dml_ccflags)
+
 ifdef CONFIG_DRM_AMD_DC_DCN2_0
+CFLAGS_display_mode_vba.o := $(dml_ccflags)
 CFLAGS_display_mode_vba_20.o := $(dml_ccflags)
 CFLAGS_display_rq_dlg_calc_20.o := $(dml_ccflags)
 endif
@@ -46,10 +47,10 @@ CFLAGS_display_rq_dlg_helpers.o := $(dml_ccflags)
 CFLAGS_dml_common_defs.o := $(dml_ccflags)
 
 DML = display_mode_lib.o display_rq_dlg_helpers.o dml1_display_rq_dlg_calc.o \
-	dml_common_defs.o display_mode_vba.o
+	dml_common_defs.o
 
 ifdef CONFIG_DRM_AMD_DC_DCN2_0
-DML += dcn20/display_rq_dlg_calc_20.o dcn20/display_mode_vba_20.o
+DML += display_mode_vba.o dcn20/display_rq_dlg_calc_20.o dcn20/display_mode_vba_20.o
 endif
 
 AMD_DAL_DML = $(addprefix $(AMDDALPATH)/dc/dml/,$(DML))

drivers/gpu/drm/amd/display/dc/dml/display_mode_lib.h

@@ -27,7 +27,9 @@
 
 
 #include "dml_common_defs.h"
+#ifdef CONFIG_DRM_AMD_DC_DCN2_0
 #include "display_mode_vba.h"
+#endif
 
 enum dml_project {
 	DML_PROJECT_UNDEFINED,
@@ -37,6 +39,8 @@ enum dml_project {
 #endif
 };
 
+struct display_mode_lib;
+
 struct dml_funcs {
 	void (*rq_dlg_get_dlg_reg)(
 			struct display_mode_lib *mode_lib,

drivers/gpu/drm/amd/display/dc/dml/display_mode_vba.h

@@ -23,6 +23,8 @@
  *
  */
 
+#ifdef CONFIG_DRM_AMD_DC_DCN2_0
+
 #ifndef __DML2_DISPLAY_MODE_VBA_H__
 #define __DML2_DISPLAY_MODE_VBA_H__
 
@@ -847,3 +849,4 @@ double CalculateWriteBackDISPCLK(
 		unsigned int WritebackChromaLineBufferWidth);
 
 #endif /* _DML2_DISPLAY_MODE_VBA_H_ */
+#endif