ARM: dts: dra7: Add dt data for PCIe controller

Added dt data for PCIe controller. This node contains dt data for
both the DRA7 part of designware controller and for the designware core.
The documention for this node can be found @ ../bindings/pci/ti-pci.txt.

Cc: Tony Lindgren <tony@atomide.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Jingoo Han <jg1.han@samsung.com>
Cc: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>