perf: perf interface for uprobes

perf: perf interface for uprobes

 - Enhances perf probe to user space executables and libraries.
 - Enhances -F/--funcs option of "perf probe" to list possible probe points in
   an executable file or library.
 - Documents userspace probing support in perf.

[ Probing a function in the executable using function name  ]
perf probe -x /bin/zsh zfree

[ Probing a library function using function name ]
perf probe -x /lib64/libc.so.6 malloc

[ list probe-able functions in an executable ]
perf probe -F -x /bin/zsh

[ list probe-able functions in an library]
perf probe -F -x /lib/libc.so.6

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>