fix(tegra): remove dependency on CPU registers to get boot parameters

fix(tegra): remove dependency on CPU registers to get boot parameters

Commit 3e14df6f6 removed the code to clear the CPU registers X0 - X3,
which affected the Tegra platforms. Tegra platforms rely on the boot
parameters passed through custom mechanisms and do not use these
general purpose registers, but maintained sanity checks to support
legacy bootloaders. These sanity checks went out of sync due to the
code cleanup from bl31_entrypoint().

This patch removes the checks and calls the SOC specific handlers to
retrieve the boot parameters.

Change-Id: I0cf4d9c0370c33ff7715b48592b6bc0602f3c93e
Signed-off-by: Kalyani Chidambaram Vaidyanathan <kalyanic@nvidia.com>
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>