arm64: dts: ti: k3-j721s2-common-proc-board: Enable PCIe

arm64: dts: ti: k3-j721s2-common-proc-board: Enable PCIe

x1 lane PCIe slot in the common processor board is enabled and connected to
J721S2 SOM. Add PCIe DT node in common processor board to reflect the
same.

Reviewed-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Signed-off-by: Matt Ranostay <mranostay@ti.com>
Signed-off-by: Ravi Gunasekaran <r-gunasekaran@ti.com>
Reviewed-by: Roger Quadros <rogerq@kernel.org>
Link: https://lore.kernel.org/r/20230331090028.8373-9-r-gunasekaran@ti.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>