ASoC: sun8i-codec-analog: Add amplifier event to fix first delay

When playing a sound for the first time, a short delay, where the audio
file is not played, can be noticed.
On a second play (right after), the sound is played correctly.
If we wait a short time (~5 sec which corresponds to the aplay
timeout), the delay is back.

This patch fixes it by using an event on headphone amplifier.
It allows to keep the amplifier enable while playing a sound.
A delay of 700ms allows to wait that the amplifier is powered-up
before playing the sound.

Signed-off-by: Mylène Josserand <mylene.josserand@free-electrons.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Mark Brown <broonie@kernel.org>