TI_SECURE_DEVICE is used by both OMAP2+ and Keystone2 family devices,
and so when ARCH_OMAP2PLUS was used to gate off the OMAP2+ Kconfig
Keystone2 family devices lost this config option.

Move this option out of mach-omap2 Kconfig to a spot accessible by both
families. We picked arch/arm/Kconfig over the TI specific board/ti/
location as this option is not specific to our boards but rather our
architecture.

Plus at some point this option can be changed to just
SECURE_DEVICE, as having secure parts is not exclusive to TI and
so other vendors can interpret this option as needed by their device
configurations.

Fixes: a93fbf4a ("ARM: omap2+: rename config to ARCH_OMAP2PLUS and consolidate Kconfig")
Signed-off-by: NAndrew F. Davis <afd@ti.com>
Reviewed-by: NLokesh Vutla <lokeshvutla@ti.com>