ASoC: audio-graph-card: Add pm callbacks to platform driver

Set snd_soc_pm_ops for the pm ops to make sure that the ASoC level of PM
operations are going to happen. This is needed to get suspend/resume
working correctly when the audio is using audio-graph-card.

Reported-by: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>