We currently get all kinds of errors building the omap gpio driver
as a module starting with:

undefined reference to `omap2_gpio_resume_after_idle'
undefined reference to `omap2_gpio_prepare_for_idle'
...

Let's fix the issue by adding inline functions to the header.
Note that we can now also remove the two unused functions for
omap_set_gpio_debounce and omap_set_gpio_debounce_time.

Then doing rmmod on the module produces further warnings
because of missing exit related functions. Let's add those.

And finally, we can make the Kconfig entry just a tristate
option that's selected for omaps.

Cc: Javier Martinez Canillas <javier@dowhile0.org>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@linaro.org>
Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Omap no longer needs this option, mach/gpio.h is
empty.

Also remove mach/irqs.h from gpio-omap.h and
include it directly from the related omap1
gpio init files.

Otherwise omap2+ build fails for MULTI_PLATFORM.

Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
Cc: Jarkko Nikula <jarkko.nikula@bitmer.com>
Cc: Liam Girdwood <lrg@ti.com>
Cc: alsa-devel@alsa-project.org
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

This way we can remove includes of plat/gpio.h which won't work
with the single zImage support.

Note that we also remove the cpu_class_is_omap2() check
in gpio-omap.c as the drivers should not call it as we need to
make it local to arch/arm/mach-omap2 for single zImage support.

While at it, arrange the related includes in the standard way.

Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: linux-mtd@lists.infradead.org
Cc: alsa-devel@alsa-project.org
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>