ply: add dynamic tracing package using BPF

ply: add dynamic tracing package using BPF

ply is a light-weight dynamic tracer for Linux that leverages the kernel's
BPF VM in concert with kprobes/tracepoints to attach probes to arbitrary
points in the kernel.

Most tracers that generate BPF bytecode are based on the LLVM-based BCC
toolchain; ply on the other hand has no external dependencies outside libc,
making it suitable for use on constrained embedded systems.

Currently ply supports x86_64, aarch64, arm, riscv64, riscv32, powerpc,
mips(el), and mips64(el) architectures.

Further documentation, examples and implementation details may be found at:
https://github.com/iovisor/ply.

Signed-off-by: Tony Ambardar <itugrok@yahoo.com>