omap2+: Add support for hwmod specific muxing of devices

omap2+: Add support for hwmod specific muxing of devices

This allows adding hwmod specific pads dynamically during the
platform device init.

Note that we don't currently have the hwmod specific signals
listed in the hwmod data, but struct omap_hwmod_mux_info will
make that possible if necessary.

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