Add BranchPlugin.decodeBranchSrc2 for branch target configs
Add BranchPlugin.decodeBranchSrc2 for branch target configs

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