arm64: dts: ti: am654-base-board: Disable SERDES and PCIe

AM654 base board does not have any PCIe slots. Disable all the
SERDES and PCIe instances.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>