regmap-irq: Add handle_mask_sync() callback

Provide a public callback handle_mask_sync() that drivers can use when
they have more complex IRQ masking logic. The default implementation is
regmap_irq_handle_mask_sync(), used if the chip doesn't provide its own
callback.

Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Link: https://lore.kernel.org/r/e083474b3d467a86e6cb53da8072de4515bd6276.1669100542.git.william.gray@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>