Adds TFABOOT support and allows to pick QE firmware
on basis of boot source.

Signed-off-by: Pankit Garg <pankit.garg@nxp.com>
Signed-off-by: Rajesh Bhagat <rajesh.bhagat@nxp.com>
[YS: remove line continuation in quoted string]
Reviewed-by: York Sun <york.sun@nxp.com>