[POWERPC] mpc512x: Add MPC512x PSC support to MPC52xx psc driver

Add 512x support using the psc_ops framework established
with the previous patch.

All 512x PSCs share the same interrupt so add
IRQF_SHARED to irq flags.

Signed-off-by: John Rigby <jrigby@freescale.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>