mmc: pxamci: Support getting GPIO descs for RO and WP

This implements the code path for the PXAMCI hostso that
it can retrieve GPIO descriptors rather than use the
global GPIO numberspace for GPIO lines. If the GPIO
descriptor is present, it will take precedence and get
used in place of the platform data GPIO number.

We move the code around a bit so we request the card
detect first and the write protect second.

We keep the code setting the host flag for the write
protect polarity inversion semantics since the slot
GPIO core needs to be refactored to deal with this
before we can get rid of this.

Cc: Daniel Mack <daniel@zonque.org>
Cc: Robert Jarzmik <robert.jarzmik@free.fr>
Cc: Bartosz Golaszewski <brgl@bgdev.pl>
Cc: Andrea Adami <andrea.adami@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>