iio: accel: adxl345: use regmap cache for INT mapping

iio: accel: adxl345: use regmap cache for INT mapping

Use regmap cache to replace the maintenance of the interrupt mapping
state by a member variable intio. The interrupt mapping is initialized
when the driver is probed, and it is perfectly cacheable.

The patch will still leave the function set_interrupts(). A follow up
patch takes care of it, when cleaning up the INT enable register
variable.

Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
Link: https://patch.msgid.link/20250313165049.48305-2-l.rubusch@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>