gpio/nomadik: disable clocks when unused

The GPIO clock is required for register access and interrupt detection.
When interrupt detection is not required on any of the pin in a block,
the block's clock can be disabled when the registers are not being
accessed.

Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Reviewed-by: Rickard Andersson <rickard.andersson@stericsson.com>
Reviewed-by: Jonas Aberg <jonas.aberg@stericsson.com>
[Adjust for new IRQ chip core code, use only local functions]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>