[POWERPC] move_device_tree() should be __init

WARNING: vmlinux.o(.text+0x1e4c0): Section mismatch in reference from the
function .move_device_tree() to the function .init.text:.lmb_alloc_base()
The function .move_device_tree() references
the function __init .lmb_alloc_base().
This is often because .move_device_tree lacks a __init
annotation or the annotation of .lmb_alloc_base is wrong.

move_device_tree() is called from early_init_devtree() only, which is __init

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>