perf tool: Parse general/raw events from sysfs

perf tool: Parse general/raw events from sysfs

PMU can export general events to sysfs, for example,

/sys/bus/event_source/devices/uncore/events
└── cycle

Then specify the event as <pmu>:<event>,

$ sudo perf stat -a -C 0 -e uncore:cycle
^C
 Performance counter stats for 'CPU 0':

        56,547,314 uncore:cycle

Raw event can be specified as <pmu>:rXXXX

$ sudo perf stat -a -C 0 -e uncore:r0101
^C
 Performance counter stats for 'CPU 0':

             8,504 uncore:r0101

Signed-off-by: Lin Ming <ming.m.lin@intel.com>