drm/i915/ehl: Make icp_digital_port_connected() use phy instead of port

When looking at SDEISR to determine the connection status of combo
outputs, we should use the phy index rather than the port index.
Although they're usually the same thing, EHL's DDI-D (port D) is
attached to PHY-A and SDEISR doesn't even have bits for a "D" output.
It's also possible that future platforms may map DDIs (the internal
display engine programming units) to PHYs (the output handling on the IO
side) in ways where port!=phy, so let's look at the PHY index by
default.

v2: Rename to intel_combo_phy_connected.  (Lucas)

Fixes: 719d2400

 ("drm/i915/ehl: Enable DDI-D")
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191127221314.575575-2-matthew.d.roper@intel.com