libata/drivers: Add driver for Apple "MacIO" IDE controller

This is a libata driver for the "macio" IDE controller used on most Apple
PowerMac and PowerBooks. It's a libata equivalent of drivers/ide/ppc/pmac.c

It supports all the features of its predecessor, including mediabay hotplug
and suspend/resume. It should also support module load/unload.

The timing calculations have been simplified to use pre-calculated tables
compared to drivers/ide/pmac.c and it uses the new mediabay interface
provided by a previous patch.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Tejun Heo <tj@kernel.org>