YaGL: Transport improved

YaGL: Transport improved

The improvements are:

* No more mlock/munlock. We now have ioctls for locking drawable
  memory so that compile transfers could be created on host. This
  is only used by offscreen backend though
* We're now using a single buffer for marshalling instead of two: one
  for commands and one for data. Also, the buffer can now be of any
  size up to 2M, it's implemented as a page list, thus, we don't need
  to allocate contigous memory anymore

Change-Id: Ia9b716c9135df75535dc515367550c9fbcf9c737