drm/i915: Hide the atomic_read(reset_counter) behind a helper

This is principally a little bit of syntatic sugar to hide the
atomic_read()s throughout the code to retrieve the current reset_counter.
It also provides the other utility functions to check the reset state on the
already read reset_counter, so that (in later patches) we can read it once
and do multiple tests rather than risk the value changing between tests.

v2: Be more strict on converting existing i915_reset_in_progress() over to
the more verbose i915_reset_in_progress_or_wedged().

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1460565315-7748-4-git-send-email-chris@chris-wilson.co.uk