ACPI: EC: Return bool from acpi_ec_dispatch_gpe()

On some systems, if suspend-to-idle is used, the EC may signal system
wakeup events (power button events, for example) as well as events
that should not cause the system to resume and acpi_ec_dispatch_gpe()
needs to be called to determine whether or not the system should
resume then.  In particular, if acpi_ec_dispatch_gpe() doesn't detect
any EC events at all, the system should remain suspended, so it is
useful to know when that is the case.

For this reason, make acpi_ec_dispatch_gpe() return a bool value
indicating whether or not any EC events have been detected by it.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>