drm/i915: split out intel_modeset_driver_remove_nogem() and simplify

Split out a separate display function for driver remove after gem
deinitialization. Note that the sequence is not symmetric with
init. However use similar naming as that reflects the deinit sequence.

No functional changes.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/197fa7e488b412e147ff0fe9440c48811888f1a6.1599056955.git.jani.nikula@intel.com