staging:iio:adc:ad7150 move from deprecated event handling plus remove irq as gpio requirement.

Another driver with some very 'non standard' magic event codes.
Again I've left it be for now and merely moved it to the new
api.

There is no reason why the irq in this driver ever had to be a gpio.
Scrap that test and clean out unecessary headers.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>