drm/i915/hotplug: Use phy to get the hpd_pin instead of the port (v5)

drm/i915/hotplug: Use phy to get the hpd_pin instead of the port (v5)

On some platforms such as Elkhart Lake, although we may use DDI D
to drive a connector, we have to use PHY A (Combo Phy PORT A) to
detect the hotplug interrupts as per the spec because there is no
one-to-one mapping between DDIs and PHYs. Therefore, use the
function intel_port_to_phy() which contains the logic for such
mapping(s) to find the correct hpd_pin.

This change should not affect other platforms as there is always
a one-to-one mapping between DDIs and PHYs.

v2:
- Convert the case statements to use PHYs instead of PORTs (Jani)

v3:
- Refactor the function to reduce the number of return statements by
  lumping all the case statements together except PHY_F which needs
  special handling (Jose)

v4:
- Add a comment describing how the HPD pin value associated with any
  port can be retrieved using port or phy enum value. (Jani)

v5:
- Use case ranges instead of individual labels and also normalize the
  return statement by adding -PHY_A to the expression (Ville)

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200304234240.12062-1-vivek.kasireddy@intel.com