- Decreased the MMC max sectors count

Some MMC cards get stuck hard when the max sectors count is >= 128.

- Add a delay after enabling the MMC power regulators

Regulator voltages typically have a rising delay. We have to make sure
the voltage has stabilized before sending the MMC init sequence.

- Add MMC cover switch last state initialization

The default last state was left to value 0 (= cover closed). If the cover
switch was initially open and then closed, no kevent about it is sent,
because the state didn't change from the last seen state.

- Add MMC transfer timeout

Very rarely the controller itself gets stuck. It needs a really hard reset
to recover. Add a timeout to work around against this.
Signed-off-by: Juha Yrjölä <juha.yrjola@nokia.com>