drm/i915: ring irq cleanups

drm/i915: ring irq cleanups

- gen6 put/get only need one argument
    rflags and gflags are always the same (see above explanation)
- remove a couple redundantly defined IRQs
- reordered some lines to make things go in descending order

Every ring has its own interrupts, enables, masks, and status bits that
are fed into the main interrupt enable/mask/status registers. At one
point in time it seemed like a good idea to make our functions support
the notion that each interrupt may have a different bit position in the
corresponding register (blitter parser error may be bit n in IMR, but
bit m in blitter IMR). It turned out though that the HW designers did us
a solid on Gen6+ and this unfortunate situation has been avoided. This
allows our interrupt code to be cleaned up a bit.

I jammed this into one commit because there should be no functional
change with this commit, and staging it into multiple commits was
unnecessarily artificial IMO.

CC: Chris Wilson <chris@chris-wilson.co.uk>
CC: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Ben Widawsky <benjamin.widawsky@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
[danvet:
- fixed up merged conflict with vlv changes.
- added GEN6 to GT blitter bit, we only use it on gen6+.
- added a comment to both ring irq bits and GT irq bits that on gen6+
  these alias.
- added comment that GT_BSD_USER_INTERRUPT is ilk-only.
- I've got confused a bit that we still use GT_USER_INTERRUPT on ivb
  for the render ring - but this goes back to ilk where we have only
  gt interrupt bits and so we be equally confusing if changed.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>