ARM: dts: bcm283x: Move ACT LED into separate dtsi

The usage of the label property for gpio-leds has been deprecated
a long time ago. In bcm2835-rpi.dtsi the ACT LED uses such a label
and derive it to almost every Raspberry Pi board. Since we cannot break
userspace interface this property must be kept. But we can move the
ACT LED into a separate dtsi and include them from the board files.

This change have two benefits:
- with both new refs it's now clear the LED part is included from a dtsi
- new boards do not include the deprecated stuff automatically

Reported-by: Alexander Dahl <ada@thorsis.com>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Link: https://lore.kernel.org/r/20221110173105.6633-3-stefan.wahren@i2se.com
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>