arm64: dts: ti: k3-am69-sk: Add PCIe support

arm64: dts: ti: k3-am69-sk: Add PCIe support

The AM69-SK board has 3 instances of PCIe namely PCIe0, PCIe1 and PCIe3.
The x4 PCIe0 instance is connected to a Card Edge connector via SERDES1.
The x2 PCIe1 instance is connected to an M.2 M Key connector via SERDES0.
The x1 PCIe3 instance is connected to an M.2 E Key connector via SERDES0.

Add device-tree support for enabling all 3 PCIe instances in Root-Complex
mode of operation.

Signed-off-by: Dasnavis Sabiya <sabiya.d@ti.com>
Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Link: https://lore.kernel.org/r/20240529082259.1619695-5-s-vadapalli@ti.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>