ASoC: twl4030: Configure extmute pinmux when the dedicated pin is in use

When HS extmute is enabled without custom GPIO we should configure the mux
to allow the pin to be used as extmute signal.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>