ARM: bcm2835: Fix names for the Raspberry Pi GPIO lines

There are some differences between the schematics and the official firmware
DTS [1]. So based on these additional information the following has been
changed:

* use consistent "CAM_GPIO1" for camera LED
* use consistent "CAM_GPIO0" for camera shutdown
* add "USB_LIMIT" for USB current limit (0=600mA, 1=1200mA)

[1] - https://github.com/raspberrypi/firmware/blob/master/extra/dt-blob.dts



Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Eric Anholt <eric@anholt.net>