serial: Update docs to indicate mcfuart supports DM_SERIAL

This driver was converted so we should remove it from the list.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/driver-model/serial-howto.txt b/doc/driver-model/serial-howto.txt
index cddfb9f..3720274 100644
--- a/doc/driver-model/serial-howto.txt
+++ b/doc/driver-model/serial-howto.txt
@@ -4,7 +4,6 @@
 Almost all of the serial drivers have been converted as at January 2016. These
 ones remain:
 
-   mcfuart.c
    serial_bfin.c
    serial_pxa.c
    serial_s3c24x0.c