ACPI / EC / PM: Close race between EC and resume from hibernation

There is a race between resume from hibernation and the EC driver
that may result in restoring the hibernation image in the middle of
an EC transaction in progress, which in turn may lead to
unpredictable behavior of the platform.

To remove that race condition, add a helpers for suspending and
resuming EC transactions in a safe way to be executed by the ACPI
platform hibernate pre-restore and restore cleanup callbacks.

http://bugzilla.kernel.org/show_bug.cgi?id=14668

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Reported-and-tested-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: Len Brown <len.brown@intel.com>