RISC-V: Refactor expand_vec_cmp [NFC]

RISC-V: Refactor expand_vec_cmp [NFC]

There are two expand_vec_cmp functions.
They have same structure and similar code.
We can use default arguments instead of overloading.

Tested on RV32 and RV64.

gcc/ChangeLog:

	* config/riscv/riscv-protos.h (expand_vec_cmp): Change proto
	* config/riscv/riscv-v.cc (expand_vec_cmp): Use default arguments
	(expand_vec_cmp_float): Adapt arguments

Signed-off-by: demin.han <demin.han@starfivetech.com>