drm/vmwgfx: Detect old user-space drivers and set up legacy emulation v2

GB aware mesa userspace drivers are detected by the fact that they are
calling the vmw getparam ioctl querying DRM_VMW_PARAM_HW_CAPS to detect
whether the device is Guest-backed object capable. For other drivers,
lie about hardware version and send the 3D capabilities in a format they
expect.

v2:
Use DRM_VMW_PARAM_MAX_MOB_MEMORY to detect gb awareness,
Make sure we don't ovwerwrite bounce buffer or write past user-space buffer
indicated size.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>