Tested by jsg@, ajacoutot@, shadchin@ and matthieu@, ok matthieu@
This diff seems larger than it is since upstream reindented some sources. This updates libdrm_intel to -current (which only affect the GEM code) and libdrm to 2.4.15. bumping both minor versions. Discussed with matthieu@
add the libdrm_intel.pc. with oga@.