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: NKishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: NRob Herring <robh@kernel.org>