Instead of driving event dispatching through a per winsys poll_dispatch
vfunc its now possible to associate a check and dispatch function with
each file descriptor that is registered for polling. This means we can
remove the winsys get_dispatch_timeout and poll_dispatch vfuncs and it
also makes it easier for more orthogonal internal components to add file
descriptors for polling to the mainloop.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
(cherry picked from commit 627947622df36dd529b9dc60a3ae9e6083532b19)
95a41e177a