drm/vmwgfx: remove code that was using physical page addresses

This code has been unused for a while now. When the explicit checks
for whether the driver is running on top of non-coherent swiotlb
have been deprecated we lost the ability to fallback to physical
mappings. Instead of trying to readd a module parameter to force
usage of physical addresses it's better to just force coherent
TTM pages via the force_coherent module parameter making this
code pointless.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Martin Krastev <krastevm@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210609172307.131929-6-zackr@vmware.com