Fix binary protocol with one serial port (#13270)

- The `sdcard.transfer_port` variable is Marlin's internal serial port index, not the physical serial port number.
- Added packet number to "ok" response so hosts don't need to wait for the ACK.
- Renamed feature to `BINARY_FILE_TRANSFER`, as the speed up is only consequential to the ability to transfer binaries over serial.

Marlin/src/gcode/host/M115.cpp

@@ -52,6 +52,13 @@ void GcodeSuite::M115() {
       #endif
     );
 
+    // BINARY_FILE_TRANSFER (M28 B1)
+    cap_line(PSTR("BINARY_FILE_TRANSFER")
+      #if ENABLED(BINARY_FILE_TRANSFER)
+        , true
+      #endif
+    );
+
     // EEPROM (M500, M501)
     cap_line(PSTR("EEPROM")
       #if ENABLED(EEPROM_SETTINGS)