Documentation: of: Document the bindings used by Juno R1 PCIe host bridge

ARM's Juno R1 board used PLDA XpressRICH3-AXI IP to implement a PCIe host
bridge. Introduce "plda" as vendor prefix for PLDA and document the DT
bindings for PLDA XpressRICH3-AXI IP as well as ARM's Juno R1.
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>

Documentation/devicetree/bindings/pci/arm,juno-r1-pcie.txt

+* ARM Juno R1 PCIe interface
+
+This PCIe host controller is based on PLDA XpressRICH3-AXI IP
+and thus inherits all the common properties defined in plda,xpressrich3-axi.txt
+as well as the base properties defined in host-generic-pci.txt.
+
+Required properties:
+ - compatible: "arm,juno-r1-pcie"
+ - dma-coherent: The host controller bridges the AXI transactions into PCIe bus
+   in a manner that makes the DMA operations to appear coherent to the CPUs.

Documentation/devicetree/bindings/pci/plda,xpressrich3-axi.txt

+* PLDA XpressRICH3-AXI host controller
+
+The PLDA XpressRICH3-AXI host controller can be configured in a manner that
+makes it compliant with the SBSA[1] standard published by ARM Ltd. For those
+scenarios, the host-generic-pci.txt bindings apply with the following additions
+to the compatible property:
+
+Required properties:
+ - compatible: should contain "plda,xpressrich3-axi" to identify the IP used.
+
+
+[1] http://infocenter.arm.com/help/topic/com.arm.doc.den0029a/

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -168,6 +168,7 @@ pericom	Pericom Technology Inc.
 phytec	PHYTEC Messtechnik GmbH
 picochip	Picochip Ltd
 plathome	Plat'Home Co., Ltd.
+plda	PLDA
 pixcir  PIXCIR MICROELECTRONICS Co., Ltd
 powervr	PowerVR (deprecated, use img)
 qca	Qualcomm Atheros, Inc.