[Intel-gfx] Semaphore cleanups

[Ben Widawsky]

FWIW, I thought my original patch was the easiest to read, but this certainly
removes the most magic. These had a ton of input from Daniel Vetter, and Chris
Wilson. The goal is only to make the code more readable, and easier to veryify/debug.

 drivers/gpu/drm/i915/i915_debugfs.c        |   10 ++--
 drivers/gpu/drm/i915/i915_gem_execbuffer.c |    4 +-
 drivers/gpu/drm/i915/i915_reg.h            |   24 +++++++++-
 drivers/gpu/drm/i915/i915_trace.h          |   61 +++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_ringbuffer.c    |   66 +++++++++++++++------------
 drivers/gpu/drm/i915/intel_ringbuffer.h    |   57 +++++++++++++-----------
 6 files changed, 157 insertions(+), 65 deletions(-)