[POWERPC] 85xx: Fix 8548CDS reset bug

Begin with MPC8548 a new reset control register is added that asserts
HRESET_REQ to board logic.

This register is used for chip reset.

Signed-off-by: Roy Zang <tie-fei.zang@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>