PM / Domains: Remove gpd_dev_ops.active_wakeup() callback

There are no more users left of the gpd_dev_ops.active_wakeup()
callback.  All have been converted to GENPD_FLAG_ACTIVE_WAKEUP.
Hence remove the callback.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>