drm/i915: Shrink {icl_mg,tgl_dkl}_phy_ddi_buf_trans

All the values we have in {icl_mg,tgl_dkl}_phy_ddi_buf_trans
fit into u8. Shrink the types accordingly.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211006204937.30774-3-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>