drm/panel: use gpiod interface for enable GPIO

Use the new GPIO descriptor interface to handle the panel's enable GPIO.
This considerably simplifies the code.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
[treding@nvidia.com: rework to improve readability]
Signed-off-by: Thierry Reding <treding@nvidia.com>
1 file changed