mmc: tmio_mmc: power status flag doesn't have to be exposed in platform data

The controller power status flag does not have to be accessed from the
hot-plug detection code any more, it can now be removed from the platform
data and put in the controller private struct.

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