ASoC: omap-mcbsp: Single function CLKR/FSR source mux configuration

Use single function for the CLKR/FSR mux configuration.
OMAP2/3 has 6 pin configuration on McBSP1 instance, while on OMAP4
McBSP4 instance have the 6 pin configuration so the omap2_mcbsp1_mux_* is
not correct name for all support OMAP versions

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@ti.com>