drm/vmwgfx: Allow checking for gl43 contexts

To make sure we're running on top of hardware that can support
GL4.3 we need to add a way of querying for those capabilities.
DRM_VMW_PARAM_GL43 allows userspace to check for presence of
GL4.3 capable contexts.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Charmaine Lee <charmainel@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211206172620.3139754-10-zack@kde.org