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

Added dt data for PCIe PHY as a child node of ocp2scp3.
The documention for this node can be found @ ../bindings/phy/ti-phy.txt.
26.3.3 PCIe Shared PHY Subsystem Integration in vE of DRA7xx ES1.0
describes the PCIe PHY subsystem-related components integrated in the device.

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>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>