[POWERPC] Fix rheap alignment problem

Honor alignment parameter in the rheap allocator.  This is needed by
qe_lib.
Remove compile warning.

Signed-off-by: Pantelis Antoniou <pantelis@embeddedalley.com>
Signed-off-by: Li Yang <leoli@freescale.com>
Acked-by: Kumar Galak <galak@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>