omap: mux: Add new style pin multiplexing code for omap3

Initially only for 34xx. This code allows us to:

- Make the code more generic as the omap internal signal
  names can stay the same across omap generations for some
  devices

- Map mux registers to GPIO registers that is needed for
  dynamic muxing of pins during off-idle

- Override bootloader mux values via kernel cmdline using
  omap_mux=some.signa1=0x1234,some.signal2=0x1234

- View and set the mux registers via debugfs if
  CONFIG_DEBUG_FS is enabled

Cc: Mike Rapoport <mike@compulab.co.il>
Cc: Benoit Cousson <b-cousson@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>