debug: improve ftrace_ramoops for io trace [2/2]

debug: improve ftrace_ramoops for io trace [2/2]

PD#SWPL-6028

Problem:
improve ftrace_ramoops to debug bus hang

Solution:
1. in uboot
setenv initargs $initargs ramoops_io_en=1 loglevel=3;save;reset
2. in linux command line:
cat /sys/module/kernel/parameters/ramoops_io_en
to check if success.
3. after watchdog reboot, get trace data with:
cat /sys/fs/pstore/ftrace-ramoops-0

Verify:
TL1 x301

Change-Id: If1a2582b40a3ded31eedef5355eb0b8a5bf495c3
Signed-off-by: Jianxin Pan <jianxin.pan@amlogic.com>