ti: omap-common: Add Kconfig file for secure device support

ti: omap-common: Add Kconfig file for secure device support

Defines CONFIG_TI_SECURE_DEVICE which needs to be turned on
when building images for secure devices. This flag is used
to invoke the secure image creation tools for creating a
boot image that can be used on secure devices. This flag
may also be used to conditionally compile code specific
to secure devices.

This terminology will be used by all OMAP architecture devices,
hence introducing to a common location.

With the creation of Kconfig for omap-common, moved the
sourcing of the Kconfig files for the omap3/4/5 and am33xx
devices from arch/arm/KConfig to the omap-common one.

Signed-off-by: Madan Srinivas <madans@ti.com>
Signed-off-by: Daniel Allred <d-allred@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>
Tested-by: Andreas Dannenberg <dannenberg@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>