dt-bindings:iio:magnetometer:honeywell,hmc5843: txt to yaml format conversion

Mostly a straight conversion, but the txt file had an oddity.
It documented a gpios property for what appeared to be in interrupt line.
There are mainline dts that have this as interrupts, so I've converted
it to that.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Neil Brown <neilb@suse.de>
Link: https://lore.kernel.org/r/20201031184854.745828-27-jic23@kernel.org