drm/i915: Disable pipes in reverse order

drm/i915: Disable pipes in reverse order

Disable CRTC/pipes in reverse order because some features (MST in
TGL+) requires master and slave relationship between pipes, so it
should always pick the lowest pipe as master as it will be enabled
first and disable in the reverse order so the master will be the last
one to be disabled.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190823082055.5992-13-lucas.demarchi@intel.com