CVA6-SDK Makefile patch for support custom buildroot output dir

cva6-sdk.custom_buildroot_output.patch

diff --git a/Makefile b/Makefile
index a10e303..4207be7 100644
--- a/Makefile
+++ b/Makefile
@@ -6,8 +6,9 @@ RISCV    := $(ROOT)/install$(XLEN)
 DEST     := $(abspath $(RISCV))
 PATH     := $(DEST)/bin:$(PATH)
 GZIP_BIN ?= gzip
+BUILDROOT_OUT ?= $(ROOT)/buildroot/output
 
-TOOLCHAIN_PREFIX := $(ROOT)/buildroot/output/host/bin/riscv$(XLEN)-buildroot-linux-gnu-
+TOOLCHAIN_PREFIX := $(BUILDROOT_OUT)/host/bin/riscv$(XLEN)-buildroot-linux-gnu-
 CC          := $(TOOLCHAIN_PREFIX)gcc
 OBJCOPY     := $(TOOLCHAIN_PREFIX)objcopy
 MKIMAGE     := u-boot/tools/mkimage
@@ -74,8 +75,8 @@ tests: install-dir $(CC)
 	cd $(ROOT)
 
 $(CC): $(buildroot_defconfig) $(linux_defconfig) $(busybox_defconfig)
-	make -C buildroot defconfig BR2_DEFCONFIG=../$(buildroot_defconfig)
-	make -C buildroot host-gcc-final $(buildroot-mk)
+	make -C buildroot defconfig BR2_DEFCONFIG=../$(buildroot_defconfig) O=$(BUILDROOT_OUT)
+	make -C buildroot host-gcc-final $(buildroot-mk) O=$(BUILDROOT_OUT)
 
 all: $(CC) isa-sim
 
@@ -91,8 +92,8 @@ rootfs/tetris: $(CC)
 
 $(RISCV)/vmlinux: $(buildroot_defconfig) $(linux_defconfig) $(busybox_defconfig) $(CC) rootfs/cachetest.elf rootfs/tetris
 	mkdir -p $(RISCV)
-	make -C buildroot $(buildroot-mk)
-	cp buildroot/output/images/vmlinux $@
+	make -C buildroot $(buildroot-mk) O=$(BUILDROOT_OUT)
+	cp $(BUILDROOT_OUT)/images/vmlinux $@
 
 $(RISCV)/Image: $(RISCV)/vmlinux
 	$(OBJCOPY) -O binary -R .note -R .comment -S $< $@
@@ -169,7 +170,7 @@ clean:
 
 clean-all: clean
 	rm -rf $(RISCV) riscv-isa-sim/build riscv-tests/build
-	make -C buildroot clean
+	make -C buildroot clean O=$(BUILDROOT_OUT)
 
 .PHONY: gcc vmlinux images help fw_payload.bin uImage