[POWERPC] Initialize lockdep earlier

This moves lockdep_init() to before udbg_early_init() as the later
can call things that acquire spinlocks etc...  This also makes printk
safer to use earlier.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>