The cros_ec driver currently assumes that cros-ec-spi compatible device
nodes are a wakeup-source even though the wakeup-source property is not
defined.

Some Chromebooks use a separate wake pin, while others overload the
interrupt for wake and IO. With the current assumption, spurious wakes
can occur on systems that use a separate wake pin. It is planned to
update the driver to no longer assume that the EC interrupt pin should
be enabled for wake.

Add the wakeup-source property to all cros-ec-spi compatible device
nodes to signify to the driver that they should still be a valid wakeup
source.
Signed-off-by: Mark Hasemeyer <markhas@chromium.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>