dts: vt8500: Update serial nodes and disable by default in SoC files

Missing aliases for uarts on vt8500, wm8505, wm8650 added.
Nodes incorrectly labelled uart@.., changed to serial@... on all SoCs.
Set each uarts default status = "disabled" as they generally don't exist.

For each board file, we only need to enable uart0 as no other uarts are
physically present on any of these boards.

Signed-off-by: Tony Prisk <linux@prisktech.co.nz>