Add support for XZ compressed kernel

Change-Id: I42b2912b83d7af374497785820182e8b5e61d12a
(cherry picked from commit 216c04bf448190278f7388944dd765a53e69af70)
Conflicts:
	arch/arm/boot/compressed/.gitignore
	arch/arm/boot/compressed/decompress.c
	lib/decompress_bunzip2.c
	lib/decompress_unxz.c
	lib/xz/xz_dec_bcj.c
	scripts/kconfig/conf.c