bsd-user: Rewrite target system call definintion glue

bsd-user: Rewrite target system call definintion glue

Rewrite target definnitions to interface with the FreeBSD system calls.
This covers basic types (time_t, iovec, umtx_time, timespec, timeval,
rusage, rwusage) and basic defines (mmap, rusage). Also included are
FreeBSD version-specific variations.

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>