RISC-V: Add RVV FMA auto-vectorization support

RISC-V: Add RVV FMA auto-vectorization support

This patch support FMA auto-vectorization pattern. Let's RA decide
vmacc or vmadd.

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

	* config/riscv/autovec.md (fma<mode>4): New pattern.
	(*fma<mode>): Ditto.
	* config/riscv/riscv-protos.h (enum insn_type): New enum.
	(emit_vlmax_ternary_insn): New function.
	* config/riscv/riscv-v.cc (emit_vlmax_ternary_insn): Ditto.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/rvv.exp: Add ternary tests
	* gcc.target/riscv/rvv/autovec/ternop/ternop-1.c: New test.
	* gcc.target/riscv/rvv/autovec/ternop/ternop-2.c: New test.
	* gcc.target/riscv/rvv/autovec/ternop/ternop-3.c: New test.
	* gcc.target/riscv/rvv/autovec/ternop/ternop_run-1.c: New test.
	* gcc.target/riscv/rvv/autovec/ternop/ternop_run-2.c: New test.
	* gcc.target/riscv/rvv/autovec/ternop/ternop_run-3.c: New test.