YaGL: Transport improved

YaGL: Transport improved

The improvements are:

* All transport related things are now inside yagl_transport, the code
  is now concentrated in a single place instead of being scattered
  all over
* No more direct memory access and page walks from API implementation
  code, this is now done inside yagl_transport, thus, API
  implementation is transport agnostic now, function prototypes
  exactly match those of target
* Target arrays can now be accessed via pointer, again, all details
  are handled by yagl_transport. For output arrays API implementation
  also receives number of elements in an array, for input
  arrays it receives maximum number of elements and is able
  to specify how much elements are actually written in order not to
  waste bandwith by transferring excess data

Change-Id: If2689c9f8452ca2d15fe54b123fa2ac9e01a61be