fb-defio: If FBINFO_VIRTFB is defined, do not set VM_IO flag.

Most users (except sh_mobile_lcdcfb.c) get their framebuffer from
vmalloc. Setting VM_IO is not necessary as the memory obtained
from vmalloc is System RAM type and is not susceptible to PCI memory
constraints.

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>