mmc: fsl_esdhc_imx: Replace more #ifdefs by if

This builds on the previous patch by converting yet more preprocessor
macros to C ifs. This is split off so that the changes adapted from
Micheal's patch may be clearly distinguished from the ones I have
authored myself.

MMC_SUPPORTS_TUNING should really get a Kconfig conversion. And DM_GPIO
needs some -ENOSYS stubs when it isn't defined.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>