omap4: cleanup pin mux data

- separate mux settings into essential and non essential parts
- essential part is board independent as of now(so move it
  to SoC directory). Will help in having single SPL for all
  boards.
- Non-essential part(the pins not essential for u-boot to function)
  need to be phased out eventually.
- Correct mux data by aligning to the latest settings in x-loader

Signed-off-by: Aneesh V <aneesh@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>