serial: xuartps: Add some register initialisation to cdns_early_console_setup()

Add initialisation of control register and baud rate to
cdns_early_console_setup(), required when running kernel standalone
without a boot loader. Baud rate is only initialised when specified in
earlycon command-line option, otherwise it is assumed this has been
set by a boot loader. Updated Documentation/kernel-parameters.txt
accordingly.

Signed-off-by: Scott Telford <stelford@cadence.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index a4f4d69..70b51f8 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1045,11 +1045,12 @@
 			determined by the stdout-path property in device
 			tree's chosen node.
 
-		cdns,<addr>
-			Start an early, polled-mode console on a cadence serial
-			port at the specified address. The cadence serial port
-			must already be setup and configured. Options are not
-			yet supported.
+		cdns,<addr>[,options]
+			Start an early, polled-mode console on a Cadence
+			(xuartps) serial port at the specified address. Only
+			supported option is baud rate. If baud rate is not
+			specified, the serial port must already be setup and
+			configured.
 
 		uart[8250],io,<addr>[,options]
 		uart[8250],mmio,<addr>[,options]