ramips: fix pci/pcie related dtc warnings

Add the ranges property to the PCI bridges where missing. Add the unit
address to PCI bridge where missing.

Rework the complete rt3883 pci node. Drop the PCI unit nodes from the
dtsi. They are not used by any dts file and should be rather in the dts
than in the SoC dtsi. Express the PCI-PCI bridge in a clean devicetree
syntax. The ralink,pci-slot isn't used by any driver, drop it. Move the
pci interrupt controller out of the pci node. It doesn't share the same
reg and therefore should be an independent/SoC child node.

Move the pci related rt3883 pinctrl setting to the dtsi instead of
defining the very same for each rt3883 board.

If the device_type property is used for PCI units, the unit is treated
as pci bridge which it isn't. Drop it for PCI units.

Reference pci-bridges or the pci node defined in the dtsi instead of
recreating the whole node hierarchy. It allows to change the referenced
node in the dtsi without the need to touch all dts.

Fix the PCI(e) wireless unit addresses. All our PCI(e) wireless chips
are the first device on the bus. The unit address has to be the bus
address instead of the PCI vendor/device id.

Signed-off-by: Mathias Kresin <dev@kresin.me>