RISC-V: Support RVV VFWREDOSUM.VS rounding mode intrinsic API

This patch would like to support the rounding mode API for the
VFWREDOSUM.VS as the below samples

* __riscv_vfwredosum_vs_f32m1_f64m1_rm
* __riscv_vfwredosum_vs_f32m1_f64m1_rm_m

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

gcc/ChangeLog:

	* config/riscv/riscv-vector-builtins-bases.cc
	(widen_freducop): Add frm_opt_type template arg.
	(vfwredosum_frm_obj): New declaration.
	(BASE): Ditto.
	* config/riscv/riscv-vector-builtins-bases.h: Ditto.
	* config/riscv/riscv-vector-builtins-functions.def
	(vfwredosum_frm): New intrinsic function def.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/float-point-wredosum.c: New test.