ARM: OMAP2+: Prevent undefined reference to omap_secure_init

omap_secure_init() will be called from all OMAP2+ platforms during their
init_early() call. This function is in omap-secure.o so include that
in the build for these platforms.

Reported-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>