iio: light: vcnl4000: Prepare for more generic setup

iio: light: vcnl4000: Prepare for more generic setup

In order to allow the chip_spec array reference the function pointers
for interrupts, the code for these functions need to be moved above the
chip_spec array.

This is a prestep to support a more generic setup of interrupts.

Signed-off-by: Mårten Lindahl <marten.lindahl@axis.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230117190017.3789181-2-marten.lindahl@axis.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>