drm/vc4: hdmi: Increase audio MAI fifo dreq threshold

Now we wait for write responses and have a burst
size of 4, we can set the fifo threshold much higher.

Set it to 28 (of the 32 entry size) to keep fifo
fuller and reduce chance of underflow.

Signed-off-by: Dom Cobley <popcornmix@gmail.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240621152055.4180873-8-dave.stevenson@raspberrypi.com


Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>