build-target-bins.sh: include Secure Partition into the FIP image.

TOS_FW_CONFIG is used as configuration file for trusted services. In
Arm infrastructure reference design platforms StMM is used as secure
partition and the secure partition manager uses secure partition config
file to prepare the execution context for secure partition.
TOS_FW_CONFIG file has details about memory regions, device regions,
runtime execution configuration etc. This file will be used by EL3
Secure Partition manager before handing over control to secure
partition (StMM).
This patch includes the tos_fw_config file into FIP for use by EL3 SPMC
during TF-A execution.

Signed-off-by: Sayanta Pattanayak <sayanta.pattanayak@arm.com>
Change-Id: Ia014461278644b520b57c825f31b9e188873609f