ACPI 5.0/iASL: Add _SLV field to UartSerialBus macro.

Slave mode is not an actual argument to this macro, but the bit is
defined in the common serial bus descriptor. There is some concern
that there may be a "slave mode" needed for some rare UARTs, so
we add this field so that the flag can be set dynamically by the
ASL, if it is required.

source/compiler/aslrestype2s.c

@@ -1199,5 +1199,15 @@ RsDoUartSerialBusDescriptor (
         InitializerOp = RsCompleteNodeAndGetNext (InitializerOp);
     }
 
+    /*
+     * Slave Mode [Flag] (_SLV)
+     *
+     * Note: There is no SlaveMode argument to the UartSerialBus macro, but
+     * we add this name anyway to allow the flag to be set by ASL in the
+     * rare case where there is a slave mode associated with the UART.
+     */
+    RsCreateBitField (InitializerOp, ACPI_RESTAG_SLAVEMODE,
+        CurrentByteOffset + ASL_RESDESC_OFFSET (UartSerialBus.Flags), 0);
+
     return (Rnode);
 }