CORE-V: SIMD Update - Removal of redundant mask macros in riscv-opt.h

    Removed individual mask macros and replaced them with three
    SIMD macros: MASK_CV_SIMD_ONE, MASK_CV_SIMD_TWO, MASK_CV_SIMD_THREE.

    * include/opcode/riscv-opc.h: Removed redundant SIMD Mask macros and
      replaced them with three MASK macros.
    * opcodes/riscv-opc.c: Replaced corresponding mask macros to each
      instruction.

Signed-off-by: Nandni Jamnadas <nandni.jamnadas@embecosm.com>