davinci: da850: move da850_evm specific mmcsd pinmux array to board file.

The da850_mmcsd0_pins pinmux array contains pins that are specific to the
da850 evm board (the write protect and card detect GPIO pins).  Move
the array to the board file.

Signed-off-by: Michael Williamson <michael.williamson@criticallink.com>
Tested-by: Sudhakar Rajashekhara <sudhakar.raj@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>