fb-defio: Inhibit VM_IO flag to be set on vmalloc-ed framebuffers.

The framebuffers (screenbase) these drivers present are actually
vmalloc-ed pages. There is no need for them to have the VM_IO flag set.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Acked-by: Jaya Kumar <jayakumar.lkml@gmail.com>