ARM: OMAP2+: Introduce check for OP-TEE in omap_secure_init()

This check and associated flag can be used to signal the presence
of OP-TEE on the platform. This can be used to determine which
SMC calls to make to perform secure operations.

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