gpio: 104-idi-48: Migrate to the regmap-irq API

The regmap API supports IO port accessors so we can take advantage of
regmap abstractions rather than handling access to the device registers
directly in the driver.

For the 104-idi-48, we get an IRQ register with some status information
and basic masking, but it's broken down by banks rather than individual
GPIO. There are six banks (8 GPIO lines each) that correspond to the
lower six bits of the IRQ register (bits 0-5):

    Base Address + 7 (Read): IRQ Status Register/IRQ Clear
        Bit 0-5: Respective Bank IRQ Statuses
        Bit 6: IRQ Status (Active Low)
        Bit 7: IRQ Enable Status
    Base Address + 7 (Write): IRQ Enable/Disable
        Bit 0-5: Respective Bank IRQ Enable/Disable

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>