ARM: dts: stm32: Add pinmux for CM4 leds pins

ARM: dts: stm32: Add pinmux for CM4 leds pins

The GPIO H7 on boards stm32mp15xx-dkx and the GPIO D8 on boards
stm32mp15xx-ed1 are used by the coprocessor Cortex-M4.
Linux running on Cortex-A should not use the GPIO and should left
it available for the coprocessor.

Add two pinmux groups, one for each families of boards, setting
the GPIO function as Reserved (RSVD).

Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Link: https://lore.kernel.org/r/20250610152309.299438-4-antonio.borneo@foss.st.com
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>