drm/panel: simple: Support delays in panel functions

For most of the panels, we need to provide delays during various stages
of panel power up and power down. Add a structure to hold those delay
values and use them in corresponding functions.

Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>