libbpf: add support for sleepable uprobe programs

Add section mappings for u(ret)probe.s programs.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Delyan Kratunov <delyank@fb.com>
Link: https://lore.kernel.org/r/aedbc3b74f3523f00010a7b0df8f3388cca59f16.1655248076.git.delyank@fb.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>