reset: lpc18xx: get rid of global variables for restart notifier

Moving the notifier_block into the drivers priv struct allows us
to retrive the priv struct with container_of and remove the
global variables.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>