ARM: bcm2835: add dmaengine driver to device tree

This adds the definitions for the BCM2835 dmaengine driver
to the device tree. The dma-channel-mask is currently
fixed. Later it should be set via the firmware.

Signed-off-by: Florian Meier <florian.meier@koalo.de>
[swarren, fixed DT node sort order]
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>