Add support for XZ compressed kernel

Conflicts:

	.config
	arch/arm/Kconfig
	arch/arm/boot/compressed/decompress.c
	init/Kconfig
	lib/Makefile
	lib/decompress.c
	lib/decompress_bunzip2.c
	lib/decompress_unxz.c
	lib/xz/xz_dec_stream.c
	scripts/Makefile.lib
	scripts/gen_initramfs_list.sh

Change-Id: I8a319dc2d5530ea61f399d0d14073e63e6da84e3