fix(runtime): Remove hard-coded configuration of VTRC_EL2:PS

The physical address size for the second stage of translation is
currently hard-coded to a maximum of 1TB.  That doesn't work for
platforms that have more than 1TB of RAM or with a RAM start address
that is above 1TB.

This patch addresses the issue by making the configuration of
VTRC_EL2:PS based on host machine's physical address range.

Change-Id: If24c1a508054a9bf88d5f6be19c9d5d7f74c99eb
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>