dm: Remove ARM dcc from the list

Remove ARM Debug communication channel driver from the list
of not converted drivers to DM.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

doc/driver-model/serial-howto.txt

@@ -4,7 +4,6 @@ How to port a serial driver to driver model
 Almost all of the serial drivers have been converted as at January 2016. These
 ones remain:
 
-   arm_dcc.c
    mcfuart.c
    serial_bfin.c
    serial_pxa.c