Switch to use internal PLL for iMCLK

Merge series from Hui Wang <hui.wang@canonical.com>:

Taking your advice and try to enable internal PLL to get a more
accurate sample rate. And I also changed the fsl-asoc-card.c to support
the nau8822 codec, now the sound quality is pretty good on my imx6sx
EVB.

sound/soc/codecs/nau8822.c

@@ -730,6 +730,13 @@ static int nau8822_set_pll(struct snd_soc_dai *dai, int pll_id, int source,
 	    freq_out == pll_param->freq_out)
 		return 0;
 
+	if (freq_out == 0) {
+		dev_dbg(component->dev, "PLL disabled\n");
+		snd_soc_component_update_bits(component,
+			NAU8822_REG_POWER_MANAGEMENT_1, NAU8822_PLL_EN_MASK, NAU8822_PLL_OFF);
+		return 0;
+	}
+
 	fs = freq_out / 256;
 
 	ret = nau8822_calc_pll(freq_in, fs, pll_param);