CV32E40Pv2 Immediate Branch Auto-Generation Support

    * gcc/common/config/riscv/riscv-common.cc: Created XCVBI extension
      support.
    * gcc/config/riscv/riscv-opts.h: Created MASK and TARGET macros for
      XCVBI.
    * gcc/config/riscv/corev.md: Implemented cv_branch<mode> pattern
      for cv.beqimm and cv.bneimm.
    * gcc/config/riscv/riscv.md: Changed pattern priority so corev.md
      patterns run before riscv.md patterns.
    * gcc/config/riscv/constraints.md: Implemented constraints
      BI5 - signed 5-bit immediate.
    * gcc/config/riscv/predicates.md: Implemented predicate
      const_int5s_operand - signed 5 bit immediate.
    * gcc/testsuite/gcc.target/riscv/cv-bi-beqimm-compile-1.c:
      Testing auto-generation for instruction cv.beqimm at all
      optimisation levels.
    * gcc/testsuite/gcc.target/riscv/cv-bi-beqimm-compile-2.c:
      Boundary testing for instruction cv.beqimm at all
      optimisation levels.
    * gcc/testsuite/gcc.target/riscv/cv-bi-bneimm-compile-1.c:
      Testing auto-generation for instruction cv.bneimm at all
      optimisation levels.
    * gcc/testsuite/gcc.target/riscv/cv-bi-bneimm-compile-2.c:
      Boundary testing for instruction cv.bneimm at all
      optimisation levels.