i2c: mv64xxx: Add runtime PM support

To save power, gate the clock when the bus is inactive, during system
sleep, and during shutdown. On some platforms, specifically Allwinner
A13/A20, gating the clock implicitly resets the module as well. Since
the module already needs to be reset after some suspend/resume cycles,
it is simple enough to reset it during every runtime suspend/resume.

Because the bus may be used by wakeup source IRQ threads, it needs to
be functional as soon as IRQs are enabled. Thus, its system PM hooks
need to run in the noirq phase.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Tested-by: Ondrej Jirman <megous@megous.com>
Acked-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>