omap2: McBSP: Remove mux code for OMAP2420 McBSP2 and do cleanups

This 'legacy' OMAP2420 McBSP2 muxing code is currently broken after recent
conversion to new mux code. The omap_mcbsp_request calling this code is
usually called after booting whereas the omap_mux_init_signal is __init
marked so null pointer dereference would occur.

Fix this by removing the muxing code and let the bootloader or board file to
do it if necessary. Remove also omap2_mcbsp_ops as there is no use for it.

Signed-off-by: Jarkko Nikula <jhnikula@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>