plat/tegra: Enable Cortex-A53 erratum 855873 workaround

The NVidia Tegra 210 SoC contains Cortex-A53 CPUs which are affected by
erratum 855873.

Enable the workaround that TF provides to fix this erratum.

Change-Id: I6cef4ac60ae745e9ce299ee22c93b9d2c4f6c5f2
Signed-off-by: Andre Przywara <andre.przywara@arm.com>