The PMU device contains an interrupt controller, power control and
resets. The interrupt controller is a little sub-standard in that
there is no race free way to clear down pending interrupts, so we try
to avoid problems by reducing the window as much as possible, and
clearing as infrequently as possible.

The interrupt support is implemented using an IRQ domain, and the
parent interrupt referenced in the standard DT way.

The power domains and reset support is closely related - there is a
defined sequence for powering down a domain which is tightly coupled
with asserting the reset. Hence, it makes sense to group these two
together, and in order to avoid any locking contention disrupting this
sequence, we avoid the use of syscon or regmap.

This patch adds the core PMU driver: power domains must be defined in
the DT file in order to make use of them. The reset controller can
be referenced in the standard way for reset controllers.

Signed-off-by: Russell King
Signed-off-by: Andrew Lunn
Signed-off-by: Gregory CLEMENT