tools: gtracestate: fix several problems

tools: gtracestate: fix several problems

Fixed problems include:
  * previously just print out a error instead of help info
    while running without cmdline parameters.
  * -u & -n lead to Segmentation fault.
  * -c and then use default ranges, the default ranges is not
        50us... but 50000/tsc2us....

Signed-off-by: Wei Gang <gang.wei@intel.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Keir Fraser <keir@xen.org>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>