drm/i915/gen11: Convert combo PHY logic to use new 'enum phy' namespace

Convert the code that operates directly on gen11 combo PHY's to use the
new namespace.  Combo PHY registers are those named "ICL_PORT_*" plus
ICL_DPHY_CHKN.

Note that a lot of the PHY programming happens in the MIPI DSI code.
For clarity I've added a for_each_dsi_phy() to loop over the phys used
by DSI.  Since DSI always uses A & B on gen11, port=phy in all cases so
it doesn't actually matter which form we use in the DSI code.  I've used
the phy iterator in code that's explicitly working with the combo PHY,
but left the rest of the DSI code using the port iterator and namespace
to minimize patch deltas.  We can switch the rest of the DSI code over
to use phy terminology later if this winds up being too confusing.

v6: Drop an include of drm/i915_drm.h; that was previously included just
    for the definition of 'enum port' which this patch removes the need
    for.  (Jose)

Cc: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190709183934.445-4-matthew.d.roper@intel.com