TI816X: Update common omap platform files

This patch updates the common platform files with TI816X support.

The approach taken in this patch is to add TI816X as part of OMAP3 variant where
the cpu class is considered as OMAP34XX and the type is TI816X. This means, both
cpu_is_omap34xx() and cpu_is_ti816x() checks return success on TI816X.

A kernel config option CONFIG_SOC_OMAPTI816X is added under OMAP3 to include
support for TI816X build.

Signed-off-by: Hemant Pedanekar <hemantp@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>