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.

The acx565akm seems to do some unique stuff with the "enabled"
state. Specifically:
1. It seems to detect the enabled state based on how the bootloader
   left the panel.
2. It uses the enabled state to prevent certain sysfs files from
   accessing a disabled panel.

We'll leave the "enabled" state tracking for this. However, we can at
least get rid of the double-check when trying to disable.

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Sebastian Reichel <sebastian.reichel@collabora.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240503143327.RFT.v2.46.I6a51b36831a5c7b2b82bccf8c550cf0d076aa541@changeid