gpio/nomadik: don't set SLPM to 1 for non-wakeup pins

Setting GPIOs' SLPM value to 1 (WAKEUP_DISABLE) is seen to cause
increased power consumption in sleep/deep-sleep. So remove the code
which disables SLPM based on the wakeup settings and only ensure
it is on as needed.

Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Reviewed-by: Srinidhi Kasagar <srinidhi.kasagar@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>