Revert "drm/panel-simple: Support for delays between GPIO & regulator"

This reverts commit 18a1488b.

Those delays were added to support the Samsung ATNA33XC20
panel. However, we've moving that to its own panel driver and out of
panel-simple. That means we don't need the ability to specify this
delay.

NOTE: it's unlikely we want to keep this delay "just in case" some
other panel needs it. The enable-gpio and the power supply are really
supposed to be different ways to specify the same thing: the main
enable of the panel. Supporting a delay between them doesn't really
make sense.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210730084534.v2.5.Ie44e3e5b7a926392541d575ca84c56931596513f@changeid