Implemented wait in normal world

Instead of busy waiting in secure world, it is more efficient to wait
in normal world such that HLOS can schedule another task to execute
while waiting

- Added a new RPC command to wait in linux driver
- Remove wait_specific() hook in time_source, it seems can be a generic
  function.
- This patch depends on "Implemented wait in normal world" in
  optee_linuxdrver