[PATCH] Makefile: add support to build dedicated devicetree

[Kory Maincent]

Add the support to build a dedicated devicetree located in arch/$(ARCH)/dts
This devicetree does not need to be listed in the relevant devicetree
makefile.

Just run the following command to build the foo devicetree placed before
at the right path:
$ make foo.dtb

Signed-off-by: Kory Maincent <kory.maincent at bootlin.com>
---
 Makefile | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Makefile b/Makefile
index 027e31e09e..2ebeaee515 100644
--- a/Makefile
+++ b/Makefile
@@ -1136,6 +1136,12 @@ dtbs: dts/dt.dtb
 dts/dt.dtb: u-boot
 	$(Q)$(MAKE) $(build)=dts dtbs
 
+ifneq ($(wildcard $(srctree)/arch/$(ARCH)/dts/),)
+dtstree := arch/$(ARCH)/dts
+%.dtb: u-boot
+	$(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
+endif
+
 quiet_cmd_copy = COPY    $@
       cmd_copy = cp $< $@
 
-- 
2.25.1