The GPIO Chip and GPIO IRQ Chip functionality are essentially orthogonal,
so GPIO IRQ Chip implementation shouldn't touch GPIO specific
registers and vise versa.

Hence, rework omap_gpio_irq_shutdown and try to touch only irqs specific
registers:
- don't configure GPIO as input (it, actually, should be already configured
  as input).
- don't clear debounce configuration if GPIO is still used as GPIO.
  We need to take in to account here commit c9c55d92
  ("gpio/omap: fix off-mode bug: clear debounce settings on free/reset").

Also remove omap_reset_gpio() function as it is not used any more.
Signed-off-by: Grygorii Strashko <grygorii.strashko@linaro.org>
Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>