drm/msm: Clean up and enhance the output of the 'gem' debugfs node

Add headers for the 'gem' debugfs file to make it easier to remember
what all the values mean and move the list of virtual address regions
to the next line and add the name and map status to make it clearer
what we are looking at.

Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>