Mikrotik RB951 router has a buzzer on the board, which makes annoying noises
due to the interference caused by PoE input or Wifi transmission
when no GPIO pin state is set.
I added buzzer node to device's DTS in order to set deault level to 1
and to provide easier access for it.
Signed-off-by: Pavel Pernička <pernicka.pa@gmail.com>
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