ARM: BeagleBoard-x15: Add mux data

Adding the mux data, manual and virtual mode
settings for BeagleBoard-X15.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>