bus: mvebu-mbus: suspend/resume support

bus: mvebu-mbus: suspend/resume support

This commit extends the mvebu-mbus driver to provide suspend/resume
support. Since mvebu-mbus is not a platform_driver, the syscore_ops
mechanism is used to get ->suspend() and ->resume() hooks called into
the driver.

In those hooks, we save and restore the MBus windows state, to make
sure after resume all Mbus windows are properly restored. Note that
while the state of some windows could be gathered by looking again at
the Device Tree (for statically described windows), it is not the case
of dynamically described windows such as the PCIe memory and I/O
windows. Therefore, we take the simple approach of saving and
restoring the registers for all MBus windows.

In addition, the commit extends the Device Tree binding of the MBus
controller, to control the MBus bridge registers (which define which
parts of the physical address space is routed to MBus windows
vs. normal RAM memory). Those registers must be saved and restored
during suspend/resume. The Device Tree binding extension is made is a
backward compatible fashion, but of course, suspend/resume will not
work without the Device Tree update.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Link: https://lkml.kernel.org/r/1416585613-2113-7-git-send-email-thomas.petazzoni@free-electrons.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>