arm64: dts: marvell: armada-37xx: Move PCIe comphy handle property

Move the comphy handle property of the PCIe node from board specific
device tree files (EspressoBin and Turris Mox) to the generic
armada-37xx.dtsi.

This is correct since this is the only possible PCIe PHY configuration
on Armada 37xx, so when PCIe is enabled on any board, this handle is
correct.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Tested-by: Tomasz Maciej Nowak <tmn505@gmail.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>