drm/i915/dsi: remove unnecessary dsi device callbacks

Remove all the trivial and/or dummy callbacks from intel dsi device
ops. Merge send_otp_cmds into panel_reset as they're called back to
back.

This will be helpful for switching to use drm_panel for the
callbacks. If we ever need the additional callbacks, we should add them
to drm_panel funcs.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-By: Shobhit Kumar <shobhit.kumar@intel.com>
[danvet: Resolve tiny conflict with ongoing atomic work.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>