ARM: dts: omap3430-sdp: add dip switch information for MMC operation

MMC 8 bit mode operation depends on dip switch setting which is not
obvious - The current board file has this description. However, with
removal of the board file in the future, this information will be lost
and has to be rediscovered.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Benoit Cousson <bcousson@baylibre.com>