dtc: Migrate "one cell" checks to new framework

This patch converts to the new tree checking framework those checks
which verify that certain properties (#address-cells and #size-cells)
are exactly one cell in size, when present.

We also drop the old-style check for "linux,phandle" being one cell,
since that is already implied in the the existing new-style checks on
the linux,phandle property.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tests/bad-ncells.dts

@@ -0,0 +1,7 @@
+/dts-v1/;
+
+/ {
+	#address-cells = "badthing";
+	#size-cells = "badthing";
+	#interrupt-cells = "badthing";
+};