veristat: improve version reporting

For packaging version of the tool is important, so add a simple way to
specify veristat version for upstream mirror at Github.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230331222405.3468634-3-andrii@kernel.org


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