updating repo to support ps7 ddr memory

Makefile

fpga/Makefile

fpga/constraints/cva6_fpga.xdc

fpga/scripts/get_hs2_sn.tcl

fpga/scripts/program_cva6_fpga.tcl

fpga/scripts/ps7_init.tcl

fpga/scripts/run_cva6_fpga.tcl

fpga/src/cva6_zybo_z7_20.sv

fpga/src/zybo-z7-20-ddr.svh

fpga/src/zybo-z7-20.svh

fpga/xilinx/xlnx_processing_system7/Makefile

fpga/xilinx/xlnx_processing_system7/tcl/run.tcl