Moved BL2 configuration nodes from fw_config to newly
created tb_fw_config device tree.

fw_config device tree's main usage is to hold properties shared
across all BLx images.
An example is the "dtb-registry" node, which contains the
information about the other device tree configurations
(load-address, size).

Also, Updated load-address of tb_fw_config which is now located
after fw_config in SRAM.

Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Change-Id: Ic398c86a4d822dacd55b5e25fd41d4fe3888d79a