mmc: sdhci: imx: Use the slot GPIO descriptor

Simplify things by making the i.MX SDHCI driver just use
slot GPIO with descriptors instead of passing around the global
GPIO numbers that we want to get rid of.

As it turns out, just one single board is using the platform
data to pass in GPIOs numbers for CD and WP, so we augment this
to use a machine descriptor table instead.

Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: NXP Linux Team <linux-imx@nxp.com>
Cc: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>