drm/msm: Show process names in gem_describe

In $debugfs/gem we already show any vma(s) associated with an object.
Also show process names if the vma's address space is a per-process
address space.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Jordan Crouse <jcrouse@codeaurora.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>