ASoC: wm8960: Support shared LRCLK

If the LRCLK is shared and the WM8960 is clock master then we should
enable the LRCM bit to tell the device that it should drive LRCLK when
either ADC or DAC is enabled rather than separately driving the two
LRCLKs.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>