drm: use __u{32,64} instead of uint{32,64}_t in virtgpu_drm.h

Signed-off-by: Gabriel Laskar <gabriel@lse.epita.fr>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
CC: Emil Velikov <emil.l.velikov@gmail.com>
CC: Mikko Rapeli <mikko.rapeli@iki.fi>