Revert "Make using open-source drivers such as Freedreno possible."

* Holy brainmelt Batman!  I've been trying to determine what is causing
   the constant crashes for days.  It's this.  The reason is that
   enabling KGSL_DRM disables KGSL_PER_PROCESS_PAGE_TABLE! This
   configuration will cause the address space to be quickly exhausted in
   a spectacular way.

 * Please do not turn this back on unless you want to pay my
   psychiatrist bill!

This reverts commit 7a938217abd8b12e70c30bf00400fbb59dcd92a6.