dt-bindings: i2c: document st,stm32mp25-i2c compatible

Add a new compatible st,stm32mp25-i2c for the STM32MP25 series which
has only one interrupt line for both events and errors and differs in
term of handling of FastModePlus.

Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>