Documentation/kernel-parameters: add missing pciserial to the earlyprintk

The PCI based UART can be specified for earlyprintk with the 'pciserial'
parameter from the ea9e9d802. This patch adds missing information about
this parameter.

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index e9159eb98..a74d62f 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1009,6 +1009,7 @@
 			earlyprintk=serial[,0x...[,baudrate]]
 			earlyprintk=ttySn[,baudrate]
 			earlyprintk=dbgp[debugController#]
+			earlyprintk=pciserial,bus:device.function[,baudrate]
 
 			earlyprintk is useful when the kernel crashes before
 			the normal console is initialized. It is not enabled by