arm64: enable .dtbo file building for TI arm64 SoCs

Add support for building .dtso files into .dtbo binaries. Also change
the base .dtb files to contain symbols for overlay applying purposes.

Signed-off-by: Tero Kristo <t-kristo@ti.com>

arch/arm64/Makefile

@@ -127,8 +127,10 @@ Image.%: Image
 zinstall install:
 	$(Q)$(MAKE) $(build)=$(boot) $@
 
-%.dtb: scripts
-	$(Q)$(MAKE) $(build)=$(boot)/dts $(boot)/dts/$@
+%.dtb %.dtbo: dtbdir=$(patsubst %/,%,$(patsubst %./,%,$(boot)/dts/$(dir $@)))
+
+%.dtb %.dtbo: scripts
+	$(Q)$(MAKE) $(build)=$(dtbdir) $(boot)/dts/$@
 
 PHONY += dtbs dtbs_install
 

arch/arm64/boot/dts/ti/Makefile

@@ -6,4 +6,9 @@
 # Copyright (C) 2016-2018 Texas Instruments Incorporated - http://www.ti.com/
 #
 
+DTC_FLAGS += -@
+
 dtb-$(CONFIG_ARCH_K3_AM6_SOC) += k3-am654-base-board.dtb
+
+$(obj)/%.dtbo: $(src)/%.dtso FORCE
+	$(call if_changed_dep,dtc)