drm/panel: boe-himax8279d: Stop tracking prepared/enabled

As talked about in commit d2aacaf0 ("drm/panel: Check for already
prepared/enabled in drm_panel"), we want to remove needless code from
panel drivers that was storing and double-checking the
prepared/enabled state. Even if someone was relying on the
double-check before, that double-check is now in the core and not
needed in individual drivers.

NOTE: as part of this, transition the panel's direct calls to its
disable/unprepare functions in shutdown/remove to call through DRM
panel.

Cc: Jerry Han <jerry.han.hq@gmail.com>
Cc: Jitao Shi <jitao.shi@mediatek.com>
Cc: Rock Wang <rock_wang@himax.com.cn>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20240604172305.v3.1.Ia3f254ab6e04e4f7afba6c066454498c8fb01324@changeid


Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240604172305.v3.1.Ia3f254ab6e04e4f7afba6c066454498c8fb01324@changeid