Adds .ignore_pmdown_time = true to codec driver struct.

HDMI codec is currently a dummy codec and doesn't benefit from pmdown
delay. Even if in the future the codec would controll HDMI encoder, it
would still be a digital to digital interface that should have no need
for pmdown delay.
Signed-off-by: Jyri Sarha <jsarha@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>