dt-bindings: net: Remove duplicate NSP Ethernet MAC binding document

Broadcom GMAC Ethernet Controller Device Tree Bindings

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Required properties:

 - compatible:	"brcm,bgmac-nsp"

 - reg:		Address and length of the GMAC registers,

		Address and length of the GMAC IDM registers

 - reg-names:	Names of the registers.  Must have both "gmac_base" and

		"idm_base"

 - interrupts:	Interrupt number

Optional properties:

- mac-address:	See ethernet.txt file in the same directory

Examples:

gmac0: ethernet@18022000 {

	compatible = "brcm,bgmac-nsp";

	reg = <0x18022000 0x1000>,

	      <0x18110000 0x1000>;

	reg-names = "gmac_base", "idm_base";

	interrupts = <GIC_SPI 147 IRQ_TYPE_LEVEL_HIGH>;

	status = "disabled";

};