mmc: sdhci-esdhc-imx: Call mmc_of_parse()

Currently it is not possible to use 'mmc-pwrseq-simple' property with this
driver because mmc_of_parse() is never called.

mmc_of_parse() calls mmc_pwrseq_alloc() that manages MMC power sequence and
allows passing GPIOs in the devicetree to properly power/reset the Wifi
chipset.

When using mmc_of_parse() we no longer need to have custom code to request
card-detect and write-protect pins, as this can now be handled by the mmc
core.

Tested on a imx6sl-warp board where BT/Wifi is functional and also on a
imx6q-sabresd.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>