ti: omap5: Add Kconfig options for secure EMIF reservations

Adds start address and size config options for setting aside
a portion of the EMIF memory space for usage by security software
(like a secure OS/TEE). There are two sizes, a total size and a
protected size. The region is divided into protected (secure) and
unprotected (public) regions, that are contiguous and start at the
start address given. If the start address is zero, the intention
is that the region will be automatically placed at the end of the
available external DRAM space.

Signed-off-by: Daniel Allred <d-allred@ti.com>