ARM: dts: keystone: add DT bindings for PCI controller for port 0

Add common DT bindings to support PCI controller driver for port 0 on all
of the K2 SoCs that has Synopsis Designware based pcie h/w.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>