arm64: dts: ti: k3-am642-sk: Disable PCIe

AM642-SK has no PCIe slot. Disable it here.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Aswath Govindraju <a-govindraju@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/20210603142251.14563-6-kishon@ti.com