omap2+: mux: Add macro for configuring static with omap_hwmod_mux_init

Add macro for defining static pins in the board file.

We can now start implementing pin multiplexing in the platform init
code for devices that call omap_hwmod_mux_init. Currently that is
only implemented for serial.c.

Signed-off-by: Tony Lindgren <tony@atomide.com>