libio: Clean up usage of rtems_termios_device_mode

This cleans up outputUsesInterrupts usage with rtems_termios_device_mode
enum values. The outputUsesInterrupts member was typed as an int, named
as if it were a boolean value, and used as if it were a
rtems_termios_device_mode enum. In this patch, values assigned to
outputUsesInterrupts have been converted to the corresponding
rtems_termios_device_mode enum value, conversions from
deviceOutputUsesInterrupts have been made explicit, and uses of
rtems_termios_device_mode enum values with deviceOutputUsesInterrupts
have been converted to booleans.

bsps/shared/dev/serial/console-polled.c

@@ -113,7 +113,7 @@ rtems_device_driver console_open(
     NULL,                        /* setAttributes */
     NULL,                        /* stopRemoteTx */
     NULL,                        /* startRemoteTx */
-    0                            /* outputUsesInterrupts */
+    TERMIOS_POLLED               /* outputUsesInterrupts */
   };
 
   assert( minor == 0 );