ARM: OMAP2+: Add omap_secure_init callback hook for secure initialization

This can be used for detecting secure features or making early device
init sequence changes based on device security type.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>