Add FreeBSD, NetBSD and OpenBSD values for the various signal info types
and defines to decode different signals to discover more information
about the specific signal types.

Signed-off-by: Stacey Son <sson@FreeBSD.org>
Signed-off-by: Warner Losh <imp@bsdimp.com>
Acked-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Kyle Evans <kevans@FreeBSD.org>