drm/bridge/sii8620: add continuations to messages

Due to asynchronous nature of MHL flow of execution is dispersed.
Logical continuation of some actions happens after response of peer,
i.e in interrupt handler. To simplify coding continuation mechanism
has been added - it is now possible to provide continuation callback,
which will be called after peer responds to given action.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1485935272-17337-5-git-send-email-a.hajda@samsung.com