dt-bindings: iio: humidity: hts221: support active-low interrupts

Update hts221 device binding with active-low interrupts support
(IRQ_TYPE_LEVEL_LOW and IRQ_TYPE_EDGE_FALLING).

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@st.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/humidity/hts221.txt

@@ -7,7 +7,8 @@ Required properties:
 Optional properties:
 - interrupt-parent: should be the phandle for the interrupt controller
 - interrupts: interrupt mapping for IRQ. It should be configured with
-  flags IRQ_TYPE_LEVEL_HIGH or IRQ_TYPE_EDGE_RISING.
+  flags IRQ_TYPE_LEVEL_HIGH, IRQ_TYPE_EDGE_RISING, IRQ_TYPE_LEVEL_LOW or
+  IRQ_TYPE_EDGE_FALLING.
 
   Refer to interrupt-controller/interrupts.txt for generic interrupt
   client node bindings.