ARM: dts: bcm2835: Add VCHIQ node to the Raspberry Pi boards. (v3)

The VCHIQ firmware communication channel operates in parallel with our
other mailbox-based channel.  This is the communication channel that
exposes the firmware's media decode/encode and ISP interfaces.

Signed-off-by: Eric Anholt <eric@anholt.net>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com> (v2)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>