mmc: tmio: calculate the native hotplug condition only once

The condition, whether we have to use the native TMIO card hotplug
detection interrupt, is rather complex, it is better to only calculate it
once and store in the private data.

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