dt-bindings: i2c-stm32: document optional dmas

Add missing documentation for "dmas" and "dma-names" properties that can be
used on i2c-stm32.
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Reviewed-by: Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

Documentation/devicetree/bindings/i2c/i2c-stm32.txt

@@ -21,6 +21,8 @@ Optional properties:
   100000 and 400000.
   For STM32F7, STM32H7 and STM32MP1 SoCs, Standard-mode, Fast-mode and Fast-mode
   Plus are supported, possible values are 100000, 400000 and 1000000.
+- dmas: List of phandles to rx and tx DMA channels. Refer to stm32-dma.txt.
+- dma-names: List of dma names. Valid names are: "rx" and "tx".
 - i2c-scl-rising-time-ns: I2C SCL Rising time for the board (default: 25)
   For STM32F7, STM32H7 and STM32MP1 only.
 - i2c-scl-falling-time-ns: I2C SCL Falling time for the board (default: 10)