ARM: OMAP2+: McBSP: Correct CLKR/FSR clock source mux configuration

On OMAP2/3 McBSP1 port has 6 pin setup, while on OMAP4 the port is McBSP4.
Implement the CLKR/FSR clock mux selection for OMAP4, and make sure that
we add the correct callback for the correct port across supported OMAP
versions.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Liam Girdwood <lrg@ti.com>