If we can't find the FSBL handoff struct don't panic and just use the
defaults instead.

We still print a warning to the user to let them know what we couldn't
find it.
Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>