Pairing drm_prime_handle_from_fd with close

[Thomas Hellstrom]

Hi!

It seems like prime_handle_from_fd needs to be paired with a GEM_CLOSE 
ioctl instead of a new generic HANDLE_CLOSE ioctl.

This oversight is not really a big problem but there are two solutions:
1) Create a new ioctl called HANDLE_CLOSE or something similar.
2) Use the GEM_CLOSE ioctl, but add a driver callback for drivers that 
are not GEM-aware.

It seems like GEM_CLOSE has already spread into user-space clients, so 
unless someone tell me otherwise, I'll be using
2) for the vmwgfx prime implementation.

Thanks,
Thomas