gpio: xtensa: fix driver build

Commit cad6fade ("xtensa: clean up WSR*/RSR*/get_sr/set_sr") removed
{RSR,WSR}_CPENABLE from xtensa code, but did not fix up all users,
breaking gpio-xtensa driver build. Update gpio-xtensa to use
new xtensa_{get,set}_sr API.

Cc: stable@vger.kernel.org # v5.0+
Fixes: cad6fade

 ("xtensa: clean up WSR*/RSR*/get_sr/set_sr")
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>