Only dynamically map Trusty when needed

On platforms which use ATF BL2, Trusty is already mapped in.
If the dynamic mapping function is available, it will fail on a range
overlap, and it may not be enabled by default on all platforms.
As a result, we only enable premapping for the Tegra platform.

Bug: 124390919
Change-Id: I5e8914c55c98ee397cf634bbdc824fed8219c03b
2 files changed