drm/i915/dsi: Move logging of DSI VBT parameters to a helper function

This is a preparation patch for moving the calling of *_dphy_param_init()
out of intel_dsi_vbt_init.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190605181735.7020-1-hdegoede@redhat.com