drm/vmwgfx: Sync legacy multisampling device capability

In favor of SM4.1 multisampling capability, virtual device deprecated
old multisampling device capability. Mark legacy multisampling device
capability as dead. Rename the function that masks legacy multisample
capability to reflect that now it is masking a deprecated feature.

Signed-off-by: Deepak Rawat <drawat.floss@gmail.com>
Reviewed-by: Thomas Hellström (VMware) <thomas_os@shipmail.org>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Signed-off-by: Roland Scheidegger <sroland@vmware.com>