realtek-poe: build default config from board.json #21075

Job	Run time
Feeds Package Test Build / Test aarch64_generic	3m 21s
Feeds Package Test Build / Test arm_cortex-a15_neon-vfpv4	3m 0s
Feeds Package Test Build / Test arm_cortex-a9_vfpv3-d16	4m 12s
Feeds Package Test Build / Test i386_pentium-mmx	3m 15s
Feeds Package Test Build / Test mips_24kc	3m 28s
Feeds Package Test Build / Test mipsel_24kc	2m 52s
Feeds Package Test Build / Test powerpc_464fp	3m 8s
Feeds Package Test Build / Test powerpc_8548	4m 11s
Feeds Package Test Build / Test riscv64_riscv64	2m 55s
Feeds Package Test Build / Test x86_64	3m 45s
	34m 7s

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