Raspberry Pi VideoCore firmware driver

Required properties:

- compatible:		Should be "raspberrypi,bcm2835-firmware"
- mboxes:		Phandle to the firmware device's Mailbox.
			  (See: ../mailbox/mailbox.txt for more information)

Example:

firmware {
	compatible = "raspberrypi,bcm2835-firmware";
	mboxes = <&mailbox>;
};

Add binding for the Raspberry Pi firmware driver
dt/bindings: Add binding for the Raspberry Pi firmware driver

This driver will provide support for calls into the firmware that will
be used by other drivers like cpufreq and vc4.

Signed-off-by: Eric Anholt <96f164ad4d9b2b0dacf8ebee2bb1eeb3aa69adf1@anholt.net>
Acked-by: Stephen Warren <5ef2a23ba3aff51d1cfc8c113c1ec34b608b3b13@wwwdotorg.org>
Signed-off-by: Lee Jones <630e34333487a351a857f6b705e04d30b37c1629@linaro.org>
