mm: mark VM_IO and VM_PFNMAP VMA-s as unsupported

vmsplice doesn't work for such VMA-s.

This flags is set in a kernel function remap_pfn_range()
(remap kernel memory to userspace), which is widely used by device
drivers to provide direct access to a device memory.

Reported-by: J F <jgmb45@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>