Use DEVRAM if no more space is available in VRAM

Previous Windows drivers use mainly DEVRAM so in some environments
(like RHEV-M 4.0) VRAM is really limited.
This patch use DEVRAM as a fallback to avoid getting out of memory
conditions too earlier in such environments.

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
Acked-by: Yuri Benditovich <yuri.benditovich@daynix.com>