drm/i915: drpc debugfs update for gen6

Many of the old fields from Ironlake have gone away. Strip all those
fields, and try to update to fields people care about. RC information
isn't exactly ideal anymore. All we can guarantee when we read the
register is that we're not using forcewake, ie. the software isn't
forcing the hardware to stay awake. The downside is that in doing this
we may wait a while and that causes an unnaturally idle state on the
GPU.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=42578


Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Keith Packard <keithp@keithp.com>