omap4/5: Add support for booting with CH.

Configuration header(CH) is 512 byte header attached to an OMAP
boot image that will help ROM code to initialize clocks, SDRAM
etc and copy U-Boot directly into SDRAM. CH can help us in
by-passing SPL and directly boot U-boot, hence it's an alternative
for SPL. However, we intend to support both CH and SPL for OMAP4/5.

Initialization done through CH is limited and is not equivalent
to that done by SPL. So U-Boot has to distinguish between the
two cases and handle them accordingly. This patch takes care
of doing this.

Signed-off-by: sricharan <r.sricharan@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>