arm64: dts: marvell: fix non-existed cpu referrence in armada-ap806-dual.dtsi

armada-ap806-dual.dtsi includes armada-ap806.dtsi which describes
thermal zones for 4 cpus but only cpu0 and cpu1 only exists for dual
configuration, this makes dtb compilation fail. Fix it by removing
thermal zone nodes for non-existed cpus for dual configuration.

Signed-off-by: Vadym Kochan <vadym.kochan@plvision.eu>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>