ACPI: EC: Avoid passing redundant argument to functions

ACPI: EC: Avoid passing redundant argument to functions

After commit e1039e060045 ("ACPI: EC: add support for hardware-reduced
systems") the handle_events argument passed to ec_install_handlers()
and acpi_ec_setup() is redundant, because it is always 'false' when
the device argument passed to them in NULL and it is always 'true'
otherwise, so the device argument can be tested against NULL instead
of testing the handle_events one.

Accordingly, modify ec_install_handlers() and acpi_ec_setup() to take
two arguments and reduce the number of checks in the former.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>