MIPS: enable both vmlinux.gz.itb and vmlinuz for generic

vmlinux.gz.itb should be appended to all-$(CONFIG_MIPS_GENERIC)
instead of replacing. Otherwise, no vmlinuz will be built.
Signed-off-by: YunQiang Su <yunqiang.su@cipunited.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/generic/Platform

@@ -14,7 +14,7 @@ cflags-$(CONFIG_MIPS_GENERIC)	+= -I$(srctree)/arch/mips/include/asm/mach-generic
 
 load-$(CONFIG_MIPS_GENERIC)	+= 0xffffffff80100000
 zload-$(CONFIG_MIPS_GENERIC)	+= 0xffffffff81000000
-all-$(CONFIG_MIPS_GENERIC)	:= vmlinux.gz.itb
+all-$(CONFIG_MIPS_GENERIC)	+= vmlinux.gz.itb
 
 its-y					:= vmlinux.its.S
 its-$(CONFIG_FIT_IMAGE_FDT_BOSTON)	+= board-boston.its.S