NXP provide libdrm updated to 2.4.91
This is a constraint for mesa: we cannot use 18.2.x from Debian Stretch backports.
Also, in libdrm-imx, NXP added new defines and features and only changed the DRM_CAS define.
This define has no impact on 18.1.x mesa versions, so we cans use latest 18.1.x version from Debian snapshots:
   https://snapshot.debian.org/package/mesa/18.1.9-1~bpo9%2B1/