svga: improve check for 3D compressed textures

svga: improve check for 3D compressed textures

This is basically a a respin of f1dfcf4bce35e6796f873d9a00103b280da81e4c
per Jose's suggestion.

Just set the SVGA3dSurfaceFormatCaps flags for 3D and cube textures
when checking the texture format capabilities.  This will filter out
unsupported combinations like 3D+DXT.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>