mmc: davinci: use mmc_of_parse to parse common mmc configuration

Card detect and write protect are currently not working on a DT
boot, and the driver relies on polling to get the state
of the card. The current code depends on platform data callbacks
to register and get the state of the gpios.

mmc core provides a generic way to parse device tree configuration,
which will take care of registering the gpios for us, lets use it
so that we don't need to poll, and parse the same properties.

Signed-off-by: Axel Haslam <ahaslam@baylibre.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: David Lechner <david@lechnology.com>