ARM Platorms: Load TB_FW_CONFIG in BL1

This patch modifies the bl1_platform_setup() API to load and authenticate
TB_FW_CONFIG in BL1. The load address of the same is passed on to BL2 in
`arg0` of entrypoint info. The fvp_io_storage.c and arm_io_storage.c also
adds entries corresponding to TB_FW_CONFIG. A helper function
`arm_load_tb_fw_config()` is added to load and authenticate TB_FW_CONFIG
if present.

Change-Id: Ie7bce667b3fad2b1a083bbcbc0a773f9f04254b1
Signed-off-by: Soby Mathew <soby.mathew@arm.com>