bus: sunxi-rsb: Implement suspend/resume/shutdown callbacks

Since system firmware is likely to use the RSB bus to communicate with a
PMIC while the system is suspended, we cannot make any assumptions about
the controller state after resuming. Thus it is important to completely
reinitialize the controller.

The RSB bus needs to be ready as soon as IRQs are enabled, to handle
wakeup event IRQs coming from the PMIC. Thus it uses NOIRQ callbacks.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>