[POWERPC] Add u64 printf to bootwrapper

Add support for the 'll' (long long) printf qualifier in the powerpc zImage
bootwrapper.  This is useful for bootwrapper debugging on 64 bit platforms.

Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>