ARM: bcm2835: add I2S driver to device tree

This adds the definitions for the BCM2835 I2S driver
to the device tree. Some GPIO settings are needed for
the correct pin functions.

Signed-off-by: Florian Meier <florian.meier@koalo.de>
[swarren: fixed DT node sort order, simplified DT label name, removed
RPI .dts file changs, since use of I2S is a user-added option.]
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>