Add 520N-MX 10G example design

example/520N_MX/fpga_10g/README.md

example/520N_MX/fpga_10g/common/quartus_pro.mk

example/520N_MX/fpga_10g/fpga.qsf

example/520N_MX/fpga_10g/fpga.sdc

example/520N_MX/fpga_10g/fpga/Makefile

example/520N_MX/fpga_10g/ip/eth_xcvr.tcl

example/520N_MX/fpga_10g/ip/eth_xcvr_pll.tcl

example/520N_MX/fpga_10g/ip/eth_xcvr_reset.tcl

example/520N_MX/fpga_10g/ip/reset_release.tcl

example/520N_MX/fpga_10g/lib/eth

example/520N_MX/fpga_10g/rtl/eth_xcvr_phy_quad_wrapper.v

example/520N_MX/fpga_10g/rtl/eth_xcvr_phy_wrapper.v

example/520N_MX/fpga_10g/rtl/fpga.v

example/520N_MX/fpga_10g/rtl/fpga_core.v

example/520N_MX/fpga_10g/rtl/sync_signal.v

example/520N_MX/fpga_10g/tb/fpga_core/Makefile

example/520N_MX/fpga_10g/tb/fpga_core/test_fpga_core.py