omap: Runtime detection of OMAP35x devices

Add runtime check for these OMAP35x variations
based on the detected Si features:
  OMAP3503, OMAP3515, OMAP3525 and OMA3530.

Also, delayed the call to pr_info() into actual
variant is detected in omap3_cpuinfo()

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