drm/i915: get mode clock when reading the pipe config v9

We need this for comparing modes between configuration changes.

The tricky part is to allow us to reuse the new get_clock stuff to
recover the lvds clock on gen2/3 when neither the vbt has an lvds mode
nor the panel a (useful) EDID.

v2: try harder to calulate non-simple pixel clocks (Daniel)
    call get_clock after getting the encoder config, needed for pixel multiply
    (Jesse)
v3: drop get_clock now that the pixel_multiply has been moved into
    get_pipe_config
v4: re-add get_clock; we need to get the pixel multiplier in the
    encoder, so need to calculate the clock value after the encoder's
    get_config is called
v5: drop hsw clock_get, still needs to be written
v6: add fuzzy clock check (Daniel)
v7: wrap fuzzy clock check under !IS_HASWELL
    use port_clock field rather than a new CPU eDP clock field in crtc_config
v8: remove stale pixel_multiplier sets (Daniel)
    multiply by pixel_multiplier in 9xx clock get too (Daniel)
v9: make sure we set pixel_multiplier before calling clock_get from mode_get
    for LVDS (Daniel)

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[danvet: Add some explanation to the commit message about why we have
to jump through a few hoops. Also remove the rebase-fail hunk from
intel_sdvo.c]
[danvet: Squash in the fixup from Jesse to also call ->get_clock in
the modeset state checker.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>