ata: rb532_cf: Convert to use GPIO descriptors

Pass a GPIO descriptor for the device instead of a hardcoded
GPIO number from the global GPIO numberspace. Use gpio
descriptors throughout.

Cut the now completely unused platform data for the CF slot.

Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Waldemar Brodkorb <wbx@openadk.org>
Cc: Matt Redfearn <matt.redfearn@mips.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>