Allow to set custom DTB/OS_CALL addresses
Allow to set custom DTB/OS_CALL addresses

Setting those from command line during compilation allows
to create a custom setup without the need of modifying the
sources.

SpinalHDL/VexRiscv,SpinalHDL/VexRiscv,SpinalHDL/VexRiscv,SpinalHDL/VexRiscv,SpinalHDL/VexRiscv