drm/i915/cnl: Add support for horizontal plane flipping

CNL supports horizontal plane flipping on non-linear plane formats.

v2:
- Avoid BUG unlike elsewhere in the code (Ville)
- Hoist the rotation-tiling restriction check (Ville)

v3 (Rodrigo):
- Rebased after a while.
- Fix small indentation issues.

Bspec: 7656
Suggested-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171215213800.7896-1-rodrigo.vivi@intel.com