configs: am62x: enable secure device configs by default

Enable the CONFIG_TI_SECURE_DEVICE by default

Non-HS devices will continue to boot due to runtime device type detection.

TI's security enforcing SoCs will authenticate each binary it loads by
comparing it's signature with keys etched into the SoC during the boot
up process. The am62x family of SoCs by default will have some level of
security enforcement checking. To keep things as simple as possible,
enable the CONFIG_TI_SECURE_DEVICE options by default so all levels of
secure SoCs will work out of the box

Signed-off-by: Praneeth Bajjuri <praneeth@ti.com>
Signed-off-by: Kamlesh Gurudasani <kamlesh@ti.com>
Signed-off-by: Bryan Brattlof <bb@ti.com>