boot/arm-trusted-firmware: Add out-of-source ATF device tree support

Similarly to Uboot, this patch adds the ability to copy in and build
out-of-source device tree sources during an ATF build.

Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

boot/arm-trusted-firmware/Config.in

@@ -68,6 +68,15 @@ config BR2_TARGET_ARM_TRUSTED_FIRMWARE_PLATFORM
 	help
 	  Target plaform to build for.
 
+config BR2_TARGET_ARM_TRUSTED_FIRMWARE_CUSTOM_DTS_PATH
+	string "Device Tree Source file paths"
+	help
+	  Space-separated list of paths to device tree source files
+	  that will be copied to fdts/ before starting the build.
+
+	  To use this device tree source file, the ATF configuration
+	  file must refer to it.
+
 config BR2_TARGET_ARM_TRUSTED_FIRMWARE_FIP
 	bool "Build FIP image"
 	help

boot/arm-trusted-firmware/arm-trusted-firmware.mk

@@ -162,7 +162,12 @@ endif
 ARM_TRUSTED_FIRMWARE_MAKE_TARGETS += \
 	$(call qstrip,$(BR2_TARGET_ARM_TRUSTED_FIRMWARE_ADDITIONAL_TARGETS))
 
+ARM_TRUSTED_FIRMWARE_CUSTOM_DTS_PATH = $(call qstrip,$(BR2_TARGET_ARM_TRUSTED_FIRMWARE_CUSTOM_DTS_PATH))
+
 define ARM_TRUSTED_FIRMWARE_BUILD_CMDS
+	$(if $(ARM_TRUSTED_FIRMWARE_CUSTOM_DTS_PATH),
+		cp -f $(ARM_TRUSTED_FIRMWARE_CUSTOM_DTS_PATH) $(@D)/fdts/
+	)
 	$(ARM_TRUSTED_FIRMWARE_BUILD_FIPTOOL)
 	$(TARGET_MAKE_ENV) $(MAKE) -C $(@D) $(ARM_TRUSTED_FIRMWARE_MAKE_OPTS) \
 		$(ARM_TRUSTED_FIRMWARE_MAKE_TARGETS)