drm/i915: add runtime put/get calls at the basic places

If I add code to enable runtime PM on my Haswell machine, start a
desktop environment, then enable runtime PM, these functions will
complain that they're trying to read/write registers while the
graphics card is suspended.

v2: - Simplify i915_gem_fault changes.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
[danvet: Drop the hunk in i915_hangcheck_elapsed, it's the wrong thing
to do.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>