ASoC: codecs: adau1701: factor out firmware reset

Some runtime-determined constraints might need to be satisfied prior to
firmware loading, so the actual download and releasing the device from
reset has to be postponed. Factor it out first, so we have everything at
one place.

This also changes the behaviour in a way that adau1701_i2c_probe() will
assert the reset line, and wait for the codec probe to release it.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>