regmap: irq: Add mask invert flag for enable register

Currently, regmap will write 1 to mask_base to mask
an interrupt and write 0 to unmask it.

But some chips do not have an interrupt mask register,
and only have interrupt enable register.
Then we should write 0 to disable interrupt and 1 to enable.

So add an mask_invert flag to handle this.
If it is not set, behavior is same as previous.
If set it to 1, the mask value will be inverted
before written to mask_base

Signed-off-by: Xiaofan Tian <tianxf@marvell.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>