ARM: dts: stm32: rename LEDs nodes for stm32f769-disco

ARM: dts: stm32: rename LEDs nodes for stm32f769-disco

Associate the LED node name with the corresponding board silkscreen for
more precise identification. In fact, the board has a total of seven
LEDs, some of which are user-controllable (i. e. usr{1,2,3}), while
others are directly controlled by hardware (e. g. power, overcurrent,
...). All these LEDs are either green or red, so using the names
led-green and led-red for the two LEDs mapped in the DTS does not
simplify their identification on the board.

Moreover, this patch is a prerequisite for adding the usr3 LED, which
has not been included in the DTS.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Link: https://lore.kernel.org/r/20250217114513.1098844-1-dario.binacchi@amarulasolutions.com
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>