drm/i915: Fix various tracepoints for gen2

Gen2 doesn't have a frame counter and apparently we no longer provide
a fake .get_vblank_counter() hook for it. That means all tracepoints
calling that hook will oops. Update the tracepoints to use
intel_crtc_get_vblank_counter() which will gracefully fall back to
using the software counter. This is actually a better approach since
we now get (hopefully accurate) frame numbers in the traces.

This also gets rid of the raw driver->get_vblank_counter() calls, which
we need to do in order to switch to the per-crtc vblank vfuncs.

v2: Deal with new tracepoints
v3: Use a distinct variable name for the internal crtc iterator (Chris)

Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Fixes: 967dd484

 ("drm: remove drm_vblank_no_hw_counter assignment from driver code")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190619170842.20579-2-ville.syrjala@linux.intel.com
(cherry picked from commit 4c888e7b

)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>