i2c: omap: Use noirq system sleep pm ops to idle device for suspend

We currently get the following error with pixcir_ts driver during a
suspend resume cycle:

omap_i2c 4802a000.i2c: controller timed out
pixcir_ts 1-005c: pixcir_int_enable: can't read reg 0x34 : -110
pixcir_ts 1-005c: Failed to disable interrupt generation: -110
pixcir_ts 1-005c: Failed to stop
dpm_run_callback(): pixcir_i2c_ts_resume+0x0/0x98
[pixcir_i2c_ts] returns -110
PM: Device 1-005c failed to resume: error -110

And at least am437x based devices with pixcir_ts will fail to resume
to a touchscreen that is configured as the wakeup-source in device
tree for these devices.

This is because pixcir_ts tries to reconfigure it's registers for
noirq suspend which fails. This also leaves i2c-omap in enabled state
for suspend.

Let's fix the pixcir_ts issue and make sure i2c-omap is suspended by
adding SET_NOIRQ_SYSTEM_SLEEP_PM_OPS.

Let's also get rid of some ifdefs while at it and replace them with
__maybe_unused as SET_RUNTIME_PM_OPS and SET_NOIRQ_SYSTEM_SLEEP_PM_OPS
already deal with the various PM Kconfig options.

Reported-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Vignesh R <vigneshr@ti.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>