kbuild: SPL/TPL: generate separate asm-offsets.h for SPL and TPL

Currently generic-asm-offsets.h and asm-offsets.h are generated based
on U-Boot proper config options. The same asm-offsets headers are used
for building U-Boot SPL/TPL, which causes potential offset mismatch if
U-Boot proper has different config options from U-Boot SPL/TPL.

This commit adds:
  spl/include/generated/(generic-)asm-offsets.h
  tpl/include/generated/(generic-)asm-offsets.h

spl/include/generated/(generic-)asm-offsets.h is generated if
CONFIG_SPL=y, and included when building SPL.

tpl/include/generated/(generic-)asm-offsets.h is generated if
CONFIG_TPL=y, and included when building TPL.

They are created before Kbuild descends into SPL/TPL object directories
and builds $(obj)/dts/dt-platdata.o because $(obj)/dts/dt-platdata.c
includes a bunch of headers.

Prepend -I$(obj)/include to $(UBOOTINCLUDE) so (generic-)asm-offsets.h
is searched in {spl,tpl}/include/generated/.

Requested-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Bin Meng <bmeng.cn@gmail.com>

Kbuild

@@ -10,7 +10,7 @@ generic-offsets-file := include/generated/generic-asm-offsets.h
 always  := $(generic-offsets-file)
 targets := lib/asm-offsets.s
 
-$(obj)/$(generic-offsets-file): lib/asm-offsets.s FORCE
+$(obj)/$(generic-offsets-file): $(obj)/lib/asm-offsets.s FORCE
 	$(call filechk,offsets,__GENERIC_ASM_OFFSETS_H__)
 
 #####
@@ -25,5 +25,5 @@ targets += arch/$(ARCH)/lib/asm-offsets.s
 
 CFLAGS_asm-offsets.o := -DDO_DEPS_ONLY
 
-$(obj)/$(offsets-file): arch/$(ARCH)/lib/asm-offsets.s FORCE
+$(obj)/$(offsets-file): $(obj)/arch/$(ARCH)/lib/asm-offsets.s FORCE
 	$(call filechk,offsets,__ASM_OFFSETS_H__)

scripts/Makefile.spl

@@ -22,6 +22,8 @@ include $(srctree)/scripts/Kbuild.include
 -include include/config/auto.conf
 -include $(obj)/include/autoconf.mk
 
+UBOOTINCLUDE := -I$(obj)/include $(UBOOTINCLUDE)
+
 KBUILD_CPPFLAGS += -DCONFIG_SPL_BUILD
 ifeq ($(CONFIG_TPL_BUILD),y)
 KBUILD_CPPFLAGS += -DCONFIG_TPL_BUILD
@@ -311,7 +313,7 @@ cmd_plat = $(CC) $(c_flags) -c $< -o $(filter-out $(PHONY),$@)
 
 targets += $(obj)/dts/dt-platdata.o
 $(obj)/dts/dt-platdata.o: $(obj)/dts/dt-platdata.c \
-		include/generated/dt-structs-gen.h FORCE
+		include/generated/dt-structs-gen.h prepare FORCE
 	$(call if_changed,plat)
 
 PHONY += dts_dir
@@ -422,9 +424,13 @@ $(obj)/$(SPL_BIN): $(u-boot-spl-platdata) $(u-boot-spl-init) \
 $(sort $(u-boot-spl-init) $(u-boot-spl-main)): $(u-boot-spl-dirs) ;
 
 PHONY += $(u-boot-spl-dirs)
-$(u-boot-spl-dirs): $(u-boot-spl-platdata)
+$(u-boot-spl-dirs): $(u-boot-spl-platdata) prepare
 	$(Q)$(MAKE) $(build)=$@
 
+PHONY += prepare
+prepare:
+	$(Q)$(MAKE) $(build)=$(obj)/.
+
 quiet_cmd_cpp_lds = LDS     $@
 cmd_cpp_lds = $(CPP) -Wp,-MD,$(depfile) $(cpp_flags) $(LDPPFLAGS) -ansi \
 		-D__ASSEMBLY__ -x assembler-with-cpp -std=c99 -P -o $@ $<