pata: remove the at91 driver

This driver is orphan since commit b2026f70 ("ARM: at91: remove
at91sam9260/at91sam9g20 legacy board support"). Given that nobody cared
adding DT support to it, it probably means it's no longer used and is
thus a good candidate for removal.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Tejun Heo <tj@kernel.org>