Remove some of the unnecessary board detection from cubox-i.
Fix USB support on i.mx6

i.mx6 has two USB controllers.  Only one was initialized before
and as it is set to OTG by default the initialisation failed
leaving you with no USB at all.  By defining the number of
controllers to be two you can at least have some USB on boot
by using the non-OTG port.
Add GPIO and EXT4 commands.