ata: ahci-platform: add reset control support

Add support to get and control a list of resets for the device
as optional and shared. These resets must be kept de-asserted until
the device is enabled.

This is specified as shared because some SoCs like UniPhier series
have common reset controls with all ahci controller instances.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>