drm/vmwgfx: Remove primary memory validation against mode while creating fb

This validation is not required because user-space will send create_fb
request once the memory is allocated. This check should be performed
during mode-setting.

Signed-off-by: Deepak Rawat <drawat@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>