gpio: pl061: set initcall level to module init

Replace subsys initcall by module initcall level. Since pinctrl
driver is already launched before gpio driver. It's unnecessary
to set gpio driver in subsys init call level.

Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>
Tested-by: Dinh Nguyen <dinguyen@altera.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>