RISC-V: Change vlmul printing rule

RISC-V: Change vlmul printing rule

This patch is preparing patch for the following patch (VSETVL PASS)
support since the current vlmul printing rule is not appropriate
information for VSETVL PASS. I split this fix in a single patch.

gcc/ChangeLog:

	* config/riscv/riscv-v.cc (emit_vlmax_vsetvl): Pass through VLMUL enum
	instead of machine mode.
	* config/riscv/riscv-vector-builtins-bases.cc: Ditto.
	* config/riscv/riscv.cc (riscv_print_operand): Print LMUL by enum vlmul
	instead of machine mode.