ARM: dts: am3517: Add pinmuxing, CD and WP for MMC1

The boardboard supports card detect and write protect, so let's
enable those pins.

Signed-off-by: Derald D. Woods <woods.technical@gmail.com>
Signed-off-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>