omap: Runtime detection of Si features

The OMAP35x family has multiple variants differing
in the HW features. This patch detects these features
at runtime and prints information during the boot.

Since most of the code seemed repetitive, macros
have been used for readability.

Signed-off-by: Sanjeev Premi <premi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>