spd: trusty: memmap trusty's code memory before peeking

This patch dynamically maps the first page of trusty's code memory,
before accessing it to find out if we are running a 32-bit or 64-bit
image.

On Tegra platforms, this means we have to increase the mappings to
accomodate the new memmap entry.

Change-Id: If370d1e6cfcccd69b260134c1b462d8d17bee03d
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>