ata: add new-style AHCI platform driver for DaVinci DA850 AHCI controller

ata: add new-style AHCI platform driver for DaVinci DA850 AHCI controller

Add the new ahci_da850 host driver.

Platform changes needed to make DaVinci DA850 SATA AHCI support
fully functional are in the separate "ARM: davinci: da850: update
SATA AHCI support" commit.

Please note that this driver doesn't have the superfluous clock
control code as clock is already handled by the generic AHCI
platform library code.

Cc: Sekhar Nori <nsekhar@ti.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Tejun Heo <tj@kernel.org>