Add PCIe EP mode dt-bindings for TI's J7200 SoC.

Link: https://lore.kernel.org/r/20201210124917.24185-4-kishon@ti.comSigned-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>