kbuild: handle dtb-y and CONFIG_OF_ALL_DTBS natively in Makefile.lib

If CONFIG_OF_ALL_DTBS is enabled, "make ARCH=arm64 dtbs" compiles each
DTB twice; one from arch/arm64/boot/dts/*/Makefile and the other from
the dtb-$(CONFIG_OF_ALL_DTBS) line in arch/arm64/boot/dts/Makefile.
It could be a race problem when building DTBS in parallel.

Another minor issue is CONFIG_OF_ALL_DTBS covers only *.dts in vendor
sub-directories, so this broke when Broadcom added one more hierarchy
in arch/arm64/boot/dts/broadcom/<soc>/.

One idea to fix the issues in a clean way is to move DTB handling
to Kbuild core scripts.  Makefile.dtbinst already recognizes dtb-y
natively, so it should not hurt to do so.

Add $(dtb-y) to extra-y, and $(dtb-) as well if CONFIG_OF_ALL_DTBS is
enabled.  All clutter things in Makefiles go away.

As a bonus clean-up, I also removed dts-dirs.  Just use subdir-y
directly to traverse sub-directories.

Signed-off-by: Masahiro Yamada <[email protected]>
Acked-by: Arnd Bergmann <[email protected]>
[robh: corrected BUILTIN_DTB to CONFIG_BUILTIN_DTB]
Signed-off-by: Rob Herring <[email protected]>

scripts/Makefile.dtbinst

@@ -5,8 +5,6 @@
 # INSTALL_DTBS_PATH directory or the default location:
 #
 #   $INSTALL_PATH/dtbs/$KERNELRELEASE
-#
-# Traverse through subdirectories listed in $(dts-dirs).
 # ==========================================================================
 
 src := $(obj)
@@ -20,8 +18,8 @@ include include/config/auto.conf
 include scripts/Kbuild.include
 include $(src)/Makefile
 
-dtbinst-files	:= $(dtb-y)
-dtbinst-dirs	:= $(dts-dirs)
+dtbinst-files	:= $(sort $(dtb-y) $(if $(CONFIG_OF_ALL_DTBS), $(dtb-)))
+dtbinst-dirs	:= $(subdir-y) $(subdir-m)
 
 # Helper targets for Installing DTBs into the boot directory
 quiet_cmd_dtb_install =	INSTALL $<