defconfig: k2l_hs_evm: Add k2l_hs_evm_defconfig

Adds a dedicated defconfig to build TI K2L secure
devices and updates MAINTAINERS.

k2l_hs_evm_defconfig is created from the k2l_evm_defconfig
and removes support for SPL, as SPL is not supported on K2
HS devices. Corrects SYS_TEXT_BASE for HS devices.

Also adds TI_SECURE_DEVICE and FIT_IMAGE_POST_PROCESS to
include support for secure image creation and authentication

Signed-off-by: Madan Srinivas <madans@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Andrew F. Davis <afd@ti.com>