gpio/omap: warn if bank is not enabled on setting irq type

For OMAP devices, if a gpio is being used as an interrupt source but has
not been requested by calling gpio_request(), a call to request_irq()
may cause the kernel hang because the gpio bank may be disabled and
hence the register access will fail. To prevent such hangs, test for
this case and warn if this is detected.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Kevin Hilman <khilman@linaro.org>
Tested-by: Javier Martinez Canillas <javier@dowhile0.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>