iio: move inv_icm42600 timestamp module in common

Create new inv_sensors common modules and move inv_icm42600
timestamp module inside. This module will be used by IMUs and
also in the future by other chips.

Modify inv_icm42600 driver to use timestamp module and do some
headers cleanup.

Signed-off-by: Jean-Baptiste Maneyrol <jean-baptiste.maneyrol@tdk.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20230606162147.79667-3-inv.git-commit@tdk.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>