formats: Switch to always use the VIRGL_FORMAT enum values

This is a shot at #121 (closed)

In order to keep the changes limited and not go out of sync with Gallium too much the old PIPE_FORMAT* are replaced with defines to their VIRGL_FORMAT* counterparts and pipe_format becomes a define of "virgl_formats".

Also all the formats that are referenced in the Gallium code are added to the format list, and all code in vrend used the virgl_formats enum and type.