r600g: Implement GL_ARB_draw_indirect for EG/CM

r600g: Implement GL_ARB_draw_indirect for EG/CM

Requires Evergreen/Cayman and radeon kernel module
2.41.0 or newer.

Expected piglit fails due to hardware limitations:
* arb_draw_indirect-draw-arrays-prim-restart
  Restarts not applied for DrawArrays commands
* arb_draw_indirect-vertexid
  Base vertex offset is not included in vertex id

Marek: bump vgt_state num_dw by 3 (= space needed for one register write)

Signed-off-by: Glenn Kennard <glenn.kennard@gmail.com>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>