arm64: dts: ti: k3-j7200-common-proc-board: Enable PCIe

x2 lane PCIe slot in the common processor board is enabled and connected to
j7200 SOM. Add PCIe DT node in common processor board to reflect the
same.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20210105151421.23237-7-kishon@ti.com