To toggle an i/o bit on iMx6 I believe i need to:
1: ensure I can write to GPIO block
2: set the pad ctl register to e.g.0x1b0b0
3: set the pad mux register to the correct alt to route the bit there
4: set relevant gpio dir bit to 1
5: write 1 or 0 to the right gpio data register bit
have I missed anything, e.g. clock enable? or anything else?