android: De-stage drm_gralloc support from mesa3d
Mainline drm_gralloc has latest commit dated Fri Jul 01 19:15:32 2016
https://android.googlesource.com/platform/external/drm_gralloc/
It was also removed from AOSP tree starting from Android-10 and likely minigbm's CrOS
gralloc was proposed as replacement.
My propose is to weigh all the pros and cons, and remove support for it from mainline mesa3d.