RISC-V: Add RVV FNMA auto-vectorization support

RISC-V: Add RVV FNMA auto-vectorization support

Like FMA, Add FNMA (VNMSAC or VNMSUB) auto-vectorization support.

Signed-off-by: Juzhe-Zhong <juzhe.zhong@rivai.ai>
gcc/ChangeLog:

	* config/riscv/autovec.md (fnma<mode>4): New pattern.
	(*fnma<mode>): Ditto.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/ternop/ternop-4.c: New test.
	* gcc.target/riscv/rvv/autovec/ternop/ternop-5.c: New test.
	* gcc.target/riscv/rvv/autovec/ternop/ternop-6.c: New test.
	* gcc.target/riscv/rvv/autovec/ternop/ternop_run-4.c: New test.
	* gcc.target/riscv/rvv/autovec/ternop/ternop_run-5.c: New test.
	* gcc.target/riscv/rvv/autovec/ternop/ternop_run-6.c: New test.