drm/panel-edp: Abstract out function to set conservative timings

If we're using the generic "edp-panel" compatible string and we fail
to detect an eDP panel then we fall back to conservative timings for
powering up and powering down the panel. Abstract out the function for
setting these timings so it can be used in future patches.

No functional change expected--just code movement.

Reviewed-by: Hsin-Yi Wang <hsinyi@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240325145626.1.I659b2517d9f619d09e804e071591ecab76335dfb@changeid