Fix cv.shuffle.b.sci immediate operand

Issue #68 (closed)

The built-in for cv.shuffle.b.sci takes an 8-bit immediate operand. The top two bits decides which cv.shufflei* instruction is used. The other six bits are printed.

Files Changed:

• config/riscv/constraints.md: Added new constraints to check the top two bits.
• config/riscv/corev.md: Likewise.
• config/riscv/riscv.cc: Added new operand type for printing the bottom six bits.
• testsuite/gcc.target/riscv/cv-simd-shufflei0-sci-b-compile-1.c: Updated test.
• testsuite/gcc.target/riscv/cv-simd-shufflei1-sci-b-compile-1.c: Likewise.
• testsuite/gcc.target/riscv/cv-simd-shufflei2-sci-b-compile-1.c: Likewise.
• testsuite/gcc.target/riscv/cv-simd-shufflei3-sci-b-compile-1.c: Likewise.
• testsuite/gcc.target/riscv/cv-xcvsimd-march-compile-1.c: Likewise.