ata: ahci_mvebu: add suspend/resume support

This commit adds suspend/resume support to the ahci_mvebu driver. The
suspend hook doesn't do anything special despite calling the generic
ahci_platform_suspend_host() function. However, the resume hook has to
restore the MBus windows configuration, as well as the regret option.

Tested on Marvell Armada 388 GP.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Tejun Heo <tj@kernel.org>