lantiq: dts: overhaul PCIe nodes

lantiq: dts: overhaul PCIe nodes

- create subnode for the child PCIe bridge
- disable PCIe by default and enable where it wasn't disabled before
- move the PCIe reset gpio to the boards dts, if we have to overwrite
  a SoC wide default, we shouldn't define a SoC wide default
- Add PCIe mem range even if they aren't yet used. Don't add the PCI I/O
  range since this range is only reserved by the driver but never used.
  Most likely as a precaution to ensure no one else writes into this
  range.

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