regmap: Add generic macro to define regmap_irq

Add REGMAP_IRQ_REG macro in regmap.h to define regmap_irq
structure easily for other driver module.

Signed-off-by: Qipeng Zha <qipeng.zha@intel.com>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>