The previous bootloader is not able to pass boot params wider than
32-bits due to an oversight in the scratch register being used. A
new secure scratch register #75 has been assigned to pass the higher
bits.

This patch adds support to parse the higher bits from scratch #75
and use them in calculating the base address for the location of
the boot params.

Scratch #75 format
====================
31:16 - bl31_plat_params high address
15:0 - bl31_params high address

Change-Id: Id53c45f70a9cb370c776ed7c82ad3f2258576a80
Signed-off-by: Steven Kao <skao@nvidia.com>