plat/arm: Load and populate fw_config and tb_fw_config

Modified the code to do below changes:

1. Load tb_fw_config along with fw_config by BL1.
2. Populate fw_config device tree information in the
   BL1 to load tb_fw_config.
3. In BL2, populate fw_config information to retrieve
   the address of tb_fw_config and then tb_fw_config
   gets populated using retrieved address.
4. Avoid processing of configuration file in case of error
   value returned from "fw_config_load" function.
5. Updated entrypoint information for BL2 image so
   that it's arg0 should point to fw_config address.

Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Signed-off-by: Louis Mayencourt <louis.mayencourt@arm.com>
Change-Id: Ife6f7b673a074e7f544ee3d1bda7645fd5b2886c