powerpc: Enable kernel XZ compression option on 44x

Enable kernel XZ compression option on 44x.
Tested on a Western Digital - MyBook Live NAS.
It takes 22 seconds for the 800 MHz CPU to decompress
and boot a 2.63 MiB XZ-compressed kernel simpleImage.
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Kconfig

@@ -201,7 +201,7 @@ config PPC
 	select HAVE_IOREMAP_PROT
 	select HAVE_IRQ_EXIT_ON_IRQ_STACK
 	select HAVE_KERNEL_GZIP
-	select HAVE_KERNEL_XZ			if PPC_BOOK3S
+	select HAVE_KERNEL_XZ			if PPC_BOOK3S || 44x
 	select HAVE_KPROBES
 	select HAVE_KPROBES_ON_FTRACE
 	select HAVE_KRETPROBES