FreeBSD: ignore some includes when not building kernel

The function abd_alloc_from_pages() is used only in kernel.
Excluding sys/vm.h, and vm/vm_page.h includes avoids dependency
problems.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Martin Matuska <mm@FreeBSD.org>
Closes #16616