minigbm/msm: Add DRM_FORMAT_FLEX_IMPLEMENTATION_DEFINED for msm

minigbm/msm: Add DRM_FORMAT_FLEX_IMPLEMENTATION_DEFINED for msm

It seems to be tradition to copy a bit of code into the
resolve_format() function for everyone.  The msm driver isn't one to
break from tradition, so we'll adopt this code fragment too.

BUG=b:154782445
TEST=Hangout

Change-Id: I9e8eaf0c5a8485afea82437fd7249e24e5509b5e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/minigbm/+/2209178
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
Commit-Queue: Douglas Anderson <dianders@chromium.org>
Tested-by: Douglas Anderson <dianders@chromium.org>