UFTrace: Support for perf-CPUx.data files

[MatthewKhouzam]

From the uftrace wiki:

perf event data files

The perf-cpuX.dat files are used to read event data generated from the Linux kernel using perf_event_open system call. But it doesn't actually open real perf events but just use a dummy event to collect task-related context info like PERF_RECORD_FORK, PERF_RECORD_EXIT, PERF_RECORD_COMM and PERF_RECORD_SWITCH (if supported). Please refer 'MMAP Layout' in the man page of perf event syscall.

It would be very good to add support for this as it can add the kernel line to the flame charts and flame graphs as well as populate the control flow, cpu usage, and resources views, as well as the syscall analyses.