dt-bindings: iio: timer: stm32: add support for STM32H7

STM32H7 has slightly different triggers than previous versions.
Introduce st,stm32h7-timer-trigger compatible to handle this new variant.
Signed-off-by: NFabrice Gasnier <fabrice.gasnier@st.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NJonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/timer/stm32-timer-trigger.txt

@@ -4,7 +4,9 @@ Must be a sub-node of an STM32 Timers device tree node.
 See ../mfd/stm32-timers.txt for details about the parent node.
 
 Required parameters:
-- compatible:	Must be "st,stm32-timer-trigger".
+- compatible:	Must be one of:
+		"st,stm32-timer-trigger"
+		"st,stm32h7-timer-trigger"
 - reg:		Identify trigger hardware block.
 
 Example: