ARM: dts: vc4-kms-v3d: Always disable firmware HDMI

Both the firmware audio driver and the vc4-kms-v3d driver are capable
of providing HDMI audio, but only one should be active at any time.
The vc4-kms-v3d overlays disable the firmware audio driver, but they
also have a noaudio parameter that as well as disabling the ARM-side
HDMI audio also re-enables the firmware HDMI audio. This is not
guaranteed to work and has been seen to break the display completely.

Modify the noaudio parameters so that the firmware HDMI audio support
remains disabled.

See: https://github.com/raspberrypi/linux/issues/4651



Signed-off-by: Phil Elwell <phil@raspberrypi.com>