ARM: dts: bcm283x: Move BCM2835/6/7 specific to bcm2835-common.dtsi

As preparation we want all common BCM2711 + BCM2835/6/7 functions in
bcm283x.dtsi and all BCM2835/6/7 specific in the new
bcm2835-common.dtsi. Since i2c2 is BCM2835 specific, we also need
to move it to bcm2835-common.dtsi.

Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Acked-by: Eric Anholt <eric@anholt.net>