configs: Add configs for AM65x High Security EVM

Add new defconfig files for the AM65x High Security EVM.

This defconfigs are the same as for the non-secure part, except for:
    CONFIG_TI_SECURE_DEVICE option set to 'y'
    CONFIG_FIT_IMAGE_POST_PROCESS option set to 'y'
    CONFIG_SPL_FIT_IMAGE_POST_PROCESS option set to 'y'

Signed-off-by: Andrew F. Davis <afd@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Andreas Dannenberg <dannenberg@ti.com>