powerpc/8xx: No need to save r10 and r3 when not calling FixupDAR

r10 and r3 are only used inside FixupDAR function. So lets save them inside
that function only.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Scott Wood <scottwood@freescale.com>