ASoC: wm8804: Enable runtime PM

Currently both the oscillator and the PLL are powered up in
set_bias_level. This can be problematic when using output clocks from
the wm8804 for other devices. The snd_soc_codec_set_pll API defines that
a clock should be available once the call returns, however, with all the
clocking controlled in set_bias_level this is not currently the case.

This patch enables pm_runtime for the wm8804, enabling both the
regulators and the oscillator when the chip resumes, and enabling the
PLL in the snd_soc_codec_set_pll call. Naturally the enabling the PLL
will also cause the chip to resume.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>