drm/i915/dsi: Do panel power on + reset deassert earlier on icl+

Looks like we're trying to talk to the DSI panel even before turning
it on, on icl+. Bspec doesn't actually specify when these should be
done, but certainly we need to turn the panel on at least before
talking to it. So let's move the power on + reset deassert steps to
be the first thing we do. This is also what Windows does.

v2: s/intel_dsi_msleep/msleep/

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230608203057.23759-2-ville.syrjala@linux.intel.com