Monitor Trap Flag (MTF), is a debugging feature that cause vmexit on
certain instruction boundaries, which can be used for HVM single step.
We prefer MTF over TF, as it make TF free for guest use.

This patch try to enable MTF for single step in gdb, and keep backward
compatibility on old processor.

Pls. see MTF details @ SDM 3b 21.7.2

Thanks,


-- 
best rgds,
edwin