ACPI: EC: tweak naming in preparation for GpioInt support

In preparation for supporting reduced hardware platforms which use a
GpioInt instead of a GPE, rename some functions and constants to have
more appropriate names. No logical changes.

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