TF-TF: Store boot parameters

This patch adds support for storing fw_config and hw_config
addresses passed as arg0 and arg1 parameters in x0, x1 from
BL31.

Signed-off-by: Alexei Fedorov <Alexei.Fedorov@arm.com>
Change-Id: I58ae379bb4a7ef1b6ce60a4e252c65d34dc14464