Tegra186: handlers to get BL31 arguments from previous bootloader

Tegra186: handlers to get BL31 arguments from previous bootloader

This patch overrides the default handlers to get BL31 arguments from the
previous bootloader. The previous bootloader stores the pointer to the
arguments in PMC secure scratch register #53.

BL31 is the first component running on the CPU, as there isn't a previous
bootloader. We set the RESET_TO_BL31 flag to enable the path which assumes
that there are no input parameters passed by the previous bootloader.

Change-Id: Idacc1df292a70c9c1cb4d5c3a774bd796175d5e8
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>