qemu_v8: add uImage target

"make linux" builds the kernel but is not sufficient to prepare all
files for "make run-only". On the other hand, "make run" does a bit
too many things to be used comfortably when working on the kernel.

Therefore, add target uImage which generates the kernel image ready
to be used by U-Boot. With that, kernel development and testing can
be done with the following sequence:

 1. make
 2. Edit kernel sources
 3. make -j$(nproc) uImage
 4. make run-only
 5. Go to 2 -- repeat as needed

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/qemu_v8.mk b/qemu_v8.mk
index 74515f3..b66b001 100644
--- a/qemu_v8.mk
+++ b/qemu_v8.mk
@@ -394,6 +394,9 @@
 				-n "Linux kernel" \
 				-d $(BINARIES_PATH)/linux.bin $(KERNEL_UIMAGE)
 
+.PHONY: uImage
+uImage: $(KERNEL_UIMAGE)
+
 $(ROOTFS_UGZ): u-boot buildroot | $(BINARIES_PATH)
 	ln -sf $(ROOT)/out-br/images/rootfs.cpio.gz $(BINARIES_PATH)
 	$(MKIMAGE_PATH)/mkimage -A arm64 \