video: arm: rpi: Add brcm,bcm2711-hdmi0 compatible

The 'brcm,bcm2711-hdmi0' compatible string is used on RPi4 instead of
'brcm,bcm2835-hdmi' since the IP core was upgraded (now called VC6
instead of VC4). This has no functional change as far as u-boot driver
is concerned. So simply add the compatible string.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Tested-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Matthias Brugger <mbrugger@suse.com>