mmc: tmio_mmc: support the generic MMC GPIO card hotplug helper

If the platform specifies the TMIO_MMC_HAS_COLD_CD flag, use the generic
MMC GPIO card hotplug helper.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Chris Ball <cjb@laptop.org>