RISC-V: Support RVV VFMACC rounding mode intrinsic API

RISC-V: Support RVV VFMACC rounding mode intrinsic API

This patch would like to support the rounding mode API for the
VFMACC for the below samples.

* __riscv_vfmacc_vv_f32m1_rm
* __riscv_vfmacc_vv_f32m1_rm_m
* __riscv_vfmacc_vf_f32m1_rm
* __riscv_vfmacc_vf_f32m1_rm_m

Signed-off-by: Pan Li <pan2.li@intel.com>
gcc/ChangeLog:

	* config/riscv/riscv-vector-builtins-bases.cc
	(class vfmacc_frm): New class for vfmacc frm.
	(vfmacc_frm_obj): New declaration.
	(BASE): Ditto.
	* config/riscv/riscv-vector-builtins-bases.h: Ditto.
	* config/riscv/riscv-vector-builtins-functions.def
	(vfmacc_frm): New function definition.
	* config/riscv/riscv-vector-builtins.cc
	(function_expander::use_ternop_insn): Add frm operand support.
	* config/riscv/vector.md: Add vfmuladd to frm_mode.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/float-point-single-multiply-add.c: New test.