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.