arm-trusted-firmware-rockchip: add m0 gcc toolchain

rk3399 ATF requires arm toolchain to build the m0 pmu driver.
As OpenWrt doesn't ship this toolchain so download the prebuilt one
just like what we did in arm-trusted-firmware-mvebu.

Fixes: 5d1cb52da0 ("arm-trusted-firmware-rockchip: Update to 2.9")

Reported-by: Wurzer Juergen <wurzer.juergen@gmail.com>
Signed-off-by: Tianling Shen <cnsztl@immortalwrt.org>

package/boot/arm-trusted-firmware-rockchip/Makefile

@@ -37,6 +37,33 @@ TFA_TARGETS:= \
 	rk3328 \
 	rk3399
 
+ifeq ($(BUILD_VARIANT),rk3399)
+  M0_GCC_NAME:=gcc-arm
+  M0_GCC_RELEASE:=11.2-2022.02
+  M0_GCC_VERSION:=$(HOST_ARCH)-arm-none-eabi
+  M0_GCC_SOURCE:=$(M0_GCC_NAME)-$(M0_GCC_RELEASE)-$(M0_GCC_VERSION).tar.xz
+
+  define Download/m0-gcc
+    FILE:=$(M0_GCC_SOURCE)
+    URL:=https://developer.arm.com/-/media/Files/downloads/gnu/$(M0_GCC_RELEASE)/binrel
+  ifeq ($(HOST_ARCH),aarch64)
+    HASH:=ef1d82e5894e3908cb7ed49c5485b5b95deefa32872f79c2b5f6f5447cabf55f
+  else
+    HASH:=8c5acd5ae567c0100245b0556941c237369f210bceb196edfe5a2e7532c60326
+  endif
+  endef
+
+  define Build/Prepare
+	$(eval $(call Download,m0-gcc))
+	$(call Build/Prepare/Default)
+
+	xzcat $(DL_DIR)/$(M0_GCC_SOURCE) | $(HOST_TAR) -C $(PKG_BUILD_DIR)/ $(TAR_OPTIONS)
+  endef
+
+  TFA_MAKE_FLAGS+= \
+    M0_CROSS_COMPILE=$(PKG_BUILD_DIR)/$(M0_GCC_NAME)-$(M0_GCC_RELEASE)-$(M0_GCC_VERSION)/bin/arm-none-eabi-
+endif
+
 define Package/trusted-firmware-a/install
 	$(INSTALL_DIR) $(STAGING_DIR_IMAGE)
 	$(INSTALL_DATA) $(PKG_BUILD_DIR)/build/$(PLAT)/release/bl31/bl31.elf $(STAGING_DIR_IMAGE)/$(BUILD_VARIANT)_bl31.elf