ar71xx: change mac address initialization

target/linux/ar71xx/files/arch/mips/ar71xx/dev-ap91-eth.c

target/linux/ar71xx/files/arch/mips/ar71xx/dev-ap91-eth.h

target/linux/ar71xx/files/arch/mips/ar71xx/devices.c

target/linux/ar71xx/files/arch/mips/ar71xx/devices.h

target/linux/ar71xx/files/arch/mips/ar71xx/mach-ap81.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-ap83.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-dir-600-a1.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-dir-615-c1.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-dir-825-b1.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-eap7660d.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-mzk-w04nu.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-mzk-w300nh.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-nbg460n.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-pb42.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-pb44.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-pb92.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-rb4xx.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-rb750.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-tew-632brp.c

target/linux/ar71xx/files/arch/mips/ar71xx/mach-tl-wa901nd.c