ecore/wayland: Use sync callback to report end of ecore_wl_init().

ecore/wayland: Use sync callback to report end of ecore_wl_init().

At the end of the ecore_wl_init() function, send a sync request to the
server, and add a callback listener to the "done" event. When this event
is received, we are sure that all the registry bind requests done so
far were processed already, and that the registry and globals are
available and can be used.

Now, on the functions that request interfaces or registry, we call
_ecore_wl_init_wait(), which will check if the callback was received
already (that means that all requests inside the init were processed).
If it was not yet, then we wait until receiving that callback, before
returning the requested data.