configs: k2l: Updates u-boot env to install secure boot monitor

This patch updates the default u-boot env for K2L HS devices
to install the secure boot monitor and load the fitImage during
boot.

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