drm/i915: Nuke intel_digital_port->port

Remove intel_digital_port->port and replace its users with
intel_encoder->port. intel_encoder->port is a superset of
intel_digital_port->port, and it works correctly even for
MST encoders.

v2: Eliminate a few dp_to_dig_port()->base.port cases too (DK)

Performed with cocci:
@@
@@
struct intel_digital_port {
       ...
-       enum port port;
       ...
}

@@
struct intel_digital_port *D;
expression E;
@@
- D->port = E;

@@
struct intel_digital_port *D;
@@
- D->port
+ D->base.port

@
expression E;
@@
(
- dp_to_dig_port(E)->port
+ dp_to_dig_port(E)->base.port
|
- enc_to_dig_port(E)->port
+ to_intel_encoder(E)->port
)

@@
expression E;
@@
- to_intel_encoder(&E->base)
+ E

@@
struct intel_digital_port *D;
identifier I, M;
@@
  I = &D->base
<...
(
- D->base.M
+ I->M
|
- &D->base
+ I
)
...>

@@
identifier D;
expression E;
identifier M;
@@
 D = enc_to_dig_port(&E->base)
<...
(
- D->base.M
+ E->M
|
- &D->base
+ E
)
...>

@@
identifier D, DP;
expression E;
identifier M;
@@
 DP = enc_to_intel_dp(&E->base)
<...
(
- dp_to_dig_port(DP)->base.M
+ E->M
|
- &dp_to_dig_port(DP)->base
+ E
)
...>

@@
expression E;
identifier M;
@@
(
- enc_to_dig_port(&E->base)->base.M
+ E->M
|
- enc_to_dig_port(&E->base)->base
+ E
|
- enc_to_mst(&E->base)->primary->base.port
+ E->port
)

@@
expression E;
identifier D;
@@
- struct intel_digital_port *D = E;
... when != D

Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171109152434.32074-1-ville.syrjala@linux.intel.com