mfd: as3722: Use devm_mfd_add_devices and devm_regmap_add_irq_chip

Use devm_mfd_add_devices() for adding MFD child devices and
devm_regmap_add_irq_chip() for IRQ chip registration.

This reduces the error code path and .remove callback for removing
MFD child devices and deleting IRQ chip data.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>