mmc: omap_hsmmc: use distinctive code paths for cover / card detect logic

Mobile phones (some) have no card detect pin, but can detect if the
cover is removed. The purpose is the same; detect if card is being
added/removed, but the details differ.
When the cover is removed, it does not mean the card is gone. But it
might, since it is accessible now. It's like a warning. All the driver
does is to limit write access to the card, see protect_card flag.
In contrast, card detect notifies us after the fact, e.g.
card is gone, card is inserted. We can't take precautions, but we can
rely on those events, -- the card is really gone, or do scan the card.
To summarize there is not much code sharing between cover and card
detect, it only increases confusion. By splitting, both will be
simplified in a followup patch.

Signed-off-by: Andreas Fenkart <afenkart@gmail.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>