drm/i915/dpio: move dpio_channel and dpio_phy enums to intel_dpio_phy.h

Reduce the size of intel_display.h by moving out the dpio_channel and
dpio_phy enums.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/7c3ee7a6482540a0267f7b2974d22cab8188707a.1667383630.git.jani.nikula@intel.com