driver: serdes_debugfs: Add inject optional parameter to prbs command

commit 49acfd1e2b1ac3c42e4d485fe24cec3c842f93b7 from
git@git.assembla.com:cavium/WindRiver.linux.git

If inject is passed to prbs command, then ATF will inject TX errors
on every RX errors.

Change-Id: Id8133270371a257c5ab3c0bee99b340e83d396aa
Signed-off-by: Chandrakala Chavva <Chandrakala.Chavva@cavium.com>
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/38623


Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Reviewed-by: Chandrakala Chavva <cchavva@marvell.com>
Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>