platform/chrome: cros_ec: handle MKBP more events flag

The ChromeOS EC has support for signaling to the host that a single IRQ
can serve multiple MKBP (Matrix KeyBoard Protocol) events.

Doing this serves an optimization purpose, as it minimizes the number of
round-trips into the interrupt handling machinery, and it proves
beneficial to sensor timestamping as it keeps the desired synchronization
of event times between the two processors.

This patch adds kernel support for this EC feature, allowing the ec_irq
to loop until all events have been served.

Signed-off-by: Enrico Granata <egranata@chromium.org>
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>