This adds the GPIO names for the Raspberry Pi Zero. The GPIO lines
of the RPi Zero are almost identical to the Model A+ except:

* GPIO 35, 38, 40 and 45 are not connected
* Status LED is active low
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Eric Anholt <eric@anholt.net>