RISC-V: Rename predicate vector_gs_scale_operand_16/32 to more generic names

RISC-V: Rename predicate vector_gs_scale_operand_16/32 to more generic names

This little rename vector_gs_scale_operand_16/32 to more generic names
const_1_or_2/4_operand. So it's a little better understood when offered
for use elsewhere.

gcc/ChangeLog:

	* config/riscv/predicates.md (const_1_or_2_operand): Rename.
	(const_1_or_4_operand): Ditto.
	(vector_gs_scale_operand_16): Ditto.
	(vector_gs_scale_operand_32): Ditto.
	* config/riscv/vector-iterators.md: Adjust.