regmap: mmio: Remove unused 64-bit support code

regmap API does not support 64-bit data size, so
there is no point to have it in regmap MMIO.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230622183613.58762-4-andriy.shevchenko@linux.intel.com


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