dt-bindings: iio: adc: stm32-adc: add stm32mp13 compatibles

Add st,stm32mp13-adc-core and st,stm32mp13-adc compatibles
to support STM32MPU13 SoC.

On STM32MP13x, each ADC peripheral has a single ADC block.
These ADC peripherals, ADC1 and ADC2, are fully independent.

Main characteristics of STM32MP13x ADC:
- One interrupt line per ADC
- 6 to 12 bits resolution
- 19 channels

ADC2 instance supports two extra internal channels VDDCPU and VDDQ_DDR.
Add "vddcpu" and "vddq_ddr" internal channels names to the reserved
labels list.

Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221012142205.13041-3-olivier.moysan@foss.st.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>