regmap: mmio: Introduce IO accessors that can talk to IO port

Some users may use regmap MMIO for IO ports, and this can be done
by assigning ioreadXX()/iowriteXX() and their Big Endian counterparts
to the regmap context.

Add IO port support with a corresponding flag added.

While doing that, make sure that user won't select relaxed MMIO access
along with IO port because the latter have no relaxed variants.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: William Breathitt Gray <william.gray@linaro.org>
Link: https://lore.kernel.org/r/20220808203401.35153-4-andriy.shevchenko@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>