MIPS: Add uImage build target

Add a uImage build target for MIPS, which builds uImage.gz (a U-Boot
image of vmlinux.bin.gz), and then symlinks it to uImage. This allows
for the use of other compression algorithms in future, and is how a few
other architectures do it.

It's enabled conditionally on load-y >= 0xffffffff80000000 which
hopefully allows 64bit kernels to also work as long as the load and
entry address can be represented by the 32bit addresses in the U-Boot
image format.

Signed-off-by: James Hogan <[e-mail]>
Cc: Ralf Baechle <[e-mail]>
Cc: Florian Fainelli <[e-mail]>
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/5795/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/Makefile

···
 boot-y			:= vmlinux.bin
 boot-y			+= vmlinux.ecoff
 boot-y			+= vmlinux.srec
+ifeq ($(shell expr $(load-y) \< 0xffffffff80000000 2> /dev/null), 0)
+boot-y			+= uImage
+boot-y			+= uImage.gz
+endif
 
 # compressed boot image targets (arch/mips/boot/compressed/)
 bootz-y			:= vmlinuz
···
 	echo '  vmlinuz.ecoff        - ECOFF zboot image'
 	echo '  vmlinuz.bin          - Raw binary zboot image'
 	echo '  vmlinuz.srec         - SREC zboot image'
+	echo '  uImage               - U-Boot image'
+	echo '  uImage.gz            - U-Boot image (gzip)'
 	echo
 	echo '  These will be default as appropriate for a configured platform.'
 endef

arch/mips/boot/.gitignore

···
 zImage
 zImage.tmp
 calc_vmlinuz_load_addr
+uImage

arch/mips/boot/Makefile

···
       cmd_srec = $(OBJCOPY) -S -O srec $(strip-flags) $(VMLINUX) $@
 $(obj)/vmlinux.srec: $(VMLINUX) FORCE
 	$(call if_changed,srec)
+
+UIMAGE_LOADADDR  = $(VMLINUX_LOAD_ADDRESS)
+UIMAGE_ENTRYADDR = $(VMLINUX_ENTRY_ADDRESS)
+
+$(obj)/vmlinux.bin.gz: $(obj)/vmlinux.bin FORCE
+	$(call if_changed,gzip)
+
+targets += uImage.gz
+$(obj)/uImage.gz: $(obj)/vmlinux.bin.gz FORCE
+	$(call if_changed,uimage,gzip)
+
+targets += uImage
+$(obj)/uImage: $(obj)/uImage.gz FORCE
+	@ln -sf $(notdir $<) $@
+	@echo '  Image $@ is ready'