ARM: bcm2835: add rpi power domain driver

This patch adds support for several power domains on Raspberry Pi,
including USB (so it can be enabled even if the bootloader didn't do
it), and graphics.

This patch is the combined work of Eric Anholt (who wrote USB support
inside of the Raspberry Pi firmware driver, and wrote the non-USB
domain support) and Alexander Aring (who separated the original USB
work out from the firmware driver).

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Kevin Hilman <khilman@linaro.org>