Revert "drm/i915/edp: Allow alternate fixed mode for eDP if available."

This reverts commit dc911f5bd8aacfcf8aabd5c26c88e04c837a938e.

Per the report, no matter what display mode you select with xrandr, the
i915 driver will always select the alternate fixed mode. For the
reporter this means that the display will always run at 40Hz which is
quite annoying. This may be due to the mode comparison.

But there are some other potential issues. The choice of alt_fixed_mode
seems dubious. It's the first non-preferred mode, but there are no
guarantees that the only difference would be refresh rate. Similarly,
there may be more than one preferred mode in the probed modes list, and
the commit changes the preferred mode selection to choose the last one
on the list instead of the first.

(Note that the probed modes list is the raw, unfiltered, unsorted list
of modes from drm_add_edid_modes(), not the pretty result after a
drm_helper_probe_single_connector_modes() call.)

Finally, we already have eerily similar code in place to find the
downclock mode for DRRS that seems like could be reused here.

Back to the drawing board.

Note: This is a hand-crafted revert due to conflicts. If it fails to
backport, please just try reverting the original commit directly.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105469
Reported-by: Rune Petersen <[email protected]>
Reported-by: Mark Spencer <[email protected]>
Fixes: dc911f5bd8aa ("drm/i915/edp: Allow alternate fixed mode for eDP if available.")
Cc: Clint Taylor <[email protected]>
Cc: David Weinehall <[email protected]>
Cc: Rodrigo Vivi <[email protected]>
Cc: Paulo Zanoni <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: Jim Bride <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: Joonas Lahtinen <[email protected]>
Cc: [email protected]
Cc: <[email protected]> # v4.14+
Signed-off-by: Jani Nikula <[email protected]>
Reviewed-by: Dhinakaran Pandiyan <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
(cherry picked from commit d93fa1b47b8fcd149b5091f18385304f402a8e15)
Signed-off-by: Jani Nikula <[email protected]>

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