drm/vmwgfx: Make sure that the multisampling is off

By default SVGA device creates nonmaskable multisampling surfaces, in
which case multisampleCount of 1 means: the first quality setting
of nonmaskable multisampling surface. Lets change it to make sure
that the backends know that multisampling is really off.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>