anv: Implement VK_KHR_draw_indirect_count for gen 7+

anv: Implement VK_KHR_draw_indirect_count for gen 7+

v2: by Jason Ekstrand
  - Move out of the draw loop population of registers
    which aren't changed in it.
  - Remove dependency on ALU registers.
  - Clarify usage of PIPE_CONTROL
  - Without usage of ALU registers patch works for gen7+

v3: set pending_pipe_bits |= ANV_PIPE_RENDER_TARGET_WRITES

Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>