ARM: bcm2835: Add names for the RPi Zero GPIO lines

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>