Tegra194: memctrl: platform handler for TZDRAM setup

This patch provides the platform with flexibility to perform custom
steps during TZDRAM setup. Tegra194 platforms checks if the config
registers are locked and TZDRAM setup has already been done by the
previous bootloaders, before setting up the fence.

Change-Id: Ifee7077d4b46a7031c4568934c63e361c53a12e3
Signed-off-by: Steven Kao <skao@nvidia.com>