perf tools: Add perf_config_u64 function

perf tools: Add perf_config_u64 function

Adding perf_config_u64 function to be able to parse 'llong' values out
of config file.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: David Ahern <dsahern@gmail.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jean Pihet <jean.pihet@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-ni6gqdlvw7khp74r9htvklkb@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>