Implement SDT probe description parsing function

Implement SDT probe description parsing function

This commit adds the lttng_elf_get_sdt_probe_offsets function to find
the SDT probe matching the received arguments and parses the SDT ELF note
section to return the number of callsite for this probe as well their
offsets in the binary.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Signed-off-by: Erica Bugden <ebugden@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>