Fix: '-g' conflicts with '-c' option and update help info

Check options conflict and exit gracefully if conflict occurred.

Before applying this patch
$ dlogutil -g -c
arc = 3, optind = 3 ,Kb 0, rotate 4
ioctl: Bad file descriptor

After applying this patch, it prints help info and exit.

Change-Id: I9133398d6f67cad6aadb6224beddd75ed06ef0dc
Signed-off-by: Chengwei Yang <chengwei.yang@intel.com>