perf stat: Add stalled cycles accounting, prettify the resulting output

Add stalled cycles accounting and use it to print the "cycles stalled per
instruction" value.

Also change the unit of the cycles output from M/sec to GHz - this is more
intuitive.

Prettify the output to:

 Performance counter stats for './loop_1b_instructions':

        239.775036 task-clock               #    0.997 CPUs utilized
       761,903,912 cycles                   #    3.178 GHz
       356,620,620 stalled-cycles           #   46.81% of all cycles are idle
     1,001,578,351 instructions             #    1.31  insns per cycle
                                            #    0.36  stalled cycles per insn
            14,782 cache-references         #    0.062 M/sec
             5,694 cache-misses             #   38.520 % of all cache refs

        0.240493656  seconds time elapsed

Also adjust the --repeat output to make the percentages align vertically:

 Performance counter stats for './loop_1b_instructions' (10 runs):

        236.096793 task-clock               #    0.997 CPUs utilized             ( +-   0.011% )
       756,553,086 cycles                   #    3.204 GHz                       ( +-   0.002% )
       354,942,692 stalled-cycles           #   46.92% of all cycles are idle    ( +-   0.008% )
     1,001,389,700 instructions             #    1.32  insns per cycle
                                            #    0.35  stalled cycles per insn   ( +-   0.000% )
            10,166 cache-references         #    0.043 M/sec                     ( +-   0.742% )
               468 cache-misses             #    4.608 % of all cache refs       ( +-  13.385% )

        0.236874136  seconds time elapsed   ( +- 0.01% )

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/n/tip-uapziqny39601apdmmhoz7hk@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>