David Stevens authored Sep 03, 2019 and David Stevens committed Sep 20, 2019

This change makes a set of changes to increase the range of gbm-based
resources that can be allocated:
 - Add VIRGL_BIND_LINEAR to support linear gbm allocations.
 - Relax the bind flag argument check if VIRGL_BIND_SHARED or
   VIRGL_BIND_LINEAR is set.
 - For resources allocated from gbm, only try to create an image if one
   of the render target or sampler view bind flags is set.
 - Don't try to calculate the internal image format for external images.

This change also fixes a use-after-free that could occur if external
image creation failed.

Signed-off-by: David Stevens <stevensd@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>