pata_mpc52xx: suspend/resume support

Implement suspend and resume routines for mpc52xx ata driver.
Tested on Lite5200b with deep-sleep and low-power (not yet in-tree)
modes.

Signed-off-by: Domen Puncer <domen.puncer@telargo.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>