docs(fvp): specify correct reference of the hw_config address

TB_FW_CONFIG DT no longer contains the address of HW_CONFIG; it has
been moved to the FW_CONFIG DT since the introduction of FCONF.
Hence updated the documentation accordingly.

Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Change-Id: I37b68502a89dbd521acd99f2cb3aeb0bd36a04e0
1 file changed