gpio: pxa: handle corner case of unprobed device

In the corner case where the gpio driver probe fails, for whatever
reason, the suspend and resume handlers will still be called as they
have to be registered as syscore operations. This applies as well when
no probe was called while the driver has been built in the kernel.

Nicolas tracked this in :
https://bugzilla.kernel.org/show_bug.cgi?id=200905



Therefore, add a failsafe in these function, and test if a proper probe
succeeded and the driver is functional.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Reported-by: Nicolas Chauvet <kwizart@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>