PCI Endpoint NTB Function Device

This describes the bindings to be used when a NTB device has to be
exposed to the remote host over PCIe.

Required Properties:
 - compatible: Should be "pci-epf-ntb"
 - epcs: As defined in generic pci-epf bindings defined in pci-epf.txt
 - epc-names: As defined in generic pci-epf bindings defined in pci-epf.txt
 - vendor-id: As defined in generic pci-epf bindings defined in pci-epf.txt
 - device-id: As defined in generic pci-epf bindings defined in pci-epf.txt
 - num-mws: Specify the number of memory windows. Should not be more than 4.
 - mws-size: List of 'num-mws' entries containing size of each memory window.

Optional Properties:
 - spad-count: Specify the number of scratchpad registers to be supported
 - db-count: Specify the number of doorbell interrupts to be supported. Must
	     not be greater than 32.

Example:
Following is an example of NTB device exposed to the remote host.

ntb {
	compatible = "pci-epf-ntb";
	epcs = <&pcie0_ep>, <&pcie1_ep>;
	epc-names = "primary", "secondary";
	vendor-id = /bits/ 16 <0x104c>;
	device-id = /bits/ 16 <0xb00d>;
	num-mws = <4>;
	mws-size = <0x100000>, <0x100000>, <0x100000>, <0x100000>;
};
