ACPI / Button: Fix enabling button GPEs twice

Button GPEs have been enabled in the acpi_wake_device_init() during
boot and the button driver enables them for the second time.
Consequently, it is necessary to do

# echo disable > /sys/firmware/acpi/interrupts/gpeXXX

twice in a row to disable those GPEs via sysfs. This patch is to
remove the GPE enabling code from the button driver to avoid the
problem.

Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
[rjw: Changelog]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>