drm/i915/dpio: un-inline the vlv phy/channel mapping functions

Simplify the heavy intel_display_types.h header.

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/943dd3e9812138b1cf3ddcfde896cfec006f3847.1667383630.git.jani.nikula@intel.com