Some versions of FreeBSD now require sys/param.h for machine/pmap.h on
x86. Include them here to meet that requirement. It does no harm on
older versions, so there's no need to #ifdef it.

Signed-off-by: Muhammad Moinur Rahman <bofh@FreeBSD.org>
Reviewed-by: John Baldwin <jhb@FreeBSD.org>
Signed-off-by: Warner Losh <imp@bsdimp.com>