ata: palmld: Introduce state container

This creates a state container struct for the Palm LifeDrive
ATA controller, and puts the ATA host and the two GPIO
descriptors into this container.

This avoids using a singleton so potentially multiple
PATA interfaces can be instantiated.

Suggested-by: Marek Vasut <marek.vasut@gmail.com>
Reviewed-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>