davinci: Add MMC/SD support for da850/omap-l138

There are two instances of MMC/SD on da850/omap-l138.
Connector for the first instance is available on the
EVM. This patch adds support for this instance.

This patch also adds support for card detect and write
protect switches on da850/omap-l138 EVM.

Signed-off-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>