dt-bindings: arm: stm32: add compatible strings for Linux Automation LXA TAC gen 3

The Linux Automation LXA TAC generation 3 is built around an
OSD32MP153x SiP with CPU, RAM, PMIC, Oscillator and EEPROM.

LXA TACs are a development tool for embedded devices with a focus on
embedded Linux devices.

Add compatible for the generation 3 based on the STM32MP153c.

Signed-off-by: Leonard Göhrs <l.goehrs@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>