arm/dts: Correct Pi 4B LED values

The initial PHY LED settings are wrong Pi 4B (the correct values got
dropped somewhere along the way). The PHY declaration should arguably
go in a separate file included by bcm2711-rpi-4-b.dts, but we can
fix that as we switch over to using more of the upstream BCM2711
support in 5.4 and later.

Signed-off-by: Phil Elwell <phil@raspberrypi.org>