video: parade: configure SLP and RST GPIOs if specified in DT

Add support to configure EDP_RST GPIO and EDP_SLP GPIO,
if provided in parade DT node.

Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>