[POWERPC] rheap - eliminates internal fragments caused by alignment

The patch adds fragments caused by rh_alloc_align() back to free list, instead
of allocating the whole chunk of memory.  This will greatly improve memory
utilization managed by rheap.

It solves MURAM not enough problem with 3 UCCs enabled on MPC8323.

Signed-off-by: Li Yang <leoli@freescale.com>
Acked-by: Joakim Tjernlund <joakim.tjernlund@transmode.se>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>