drm/i915: Don't enable the DDI-IO power in the TypeC TBT-alt mode

According to the spec we should not enable the DDI-IO power domain if
the TypeC port is in the TBT-alt mode, so do that only in the other
TypeC modes or for non-TypeC ports. See the internal BSpec Index/22243.

v2:
- Add the internal BSpec reference to the log message. (José)

Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190628143635.22066-6-imre.deak@intel.com