Add debug_test to cva6

Created by: xiaoweish

• UVM testbench ready for debug_test execution
• debug_test C/ASM files ported to CVA6
• Status:
  1. debug_test runs in UVM TB, not fully passing yet as there are ~20 sub-tests in it.
  2. UVM component TB mostly complete, minor future adjustments possible
  3. Propose merging PR for collaborative debugging