ata: sata_highbank: Convert to use GPIO descriptors

This pure device tree driver is simple to convert to use
just GPIO descriptors instead of GPIO numbers. So let's
just do it.

Cc: Mark Langsdorf <mlangsdo@redhat.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>