RISC-V: Fix ugly && incorrect codes of RVV auto-vectorization

RISC-V: Fix ugly && incorrect codes of RVV auto-vectorization

1. Add movmisalign pattern for TARGET_VECTORIZE_SUPPORT_VECTOR_MISALIGNMENT
   targethook, current RISC-V has supported this target hook, we can't make
   it supported without movmisalign pattern.

2. Remove global extern of get_mask_policy_no_pred && get_tail_policy_no_pred.
   These 2 functions are comming from intrinsic builtin frameworks.
   We are sure we don't need them in auto-vectorization implementation.

3. Refine mask mode implementation.

4. We should not have "riscv_vector_" in riscv_vector namspace since it
   makes the codes inconsistent and ugly.

   For example:
   Before this patch:
   static opt_machine_mode
   riscv_get_mask_mode (machine_mode mode)
   {
     machine_mode mask_mode = VOIDmode;
     if (TARGET_VECTOR && riscv_vector::riscv_vector_get_mask_mode (mode).exists (&mask_mode))
      return mask_mode;
   ..

   After this patch:
   riscv_get_mask_mode (machine_mode mode)
   {
     machine_mode mask_mode = VOIDmode;
     if (TARGET_VECTOR && riscv_vector::get_mask_mode (mode).exists (&mask_mode))
      return mask_mode;
   ..

5. Fix fail testcase fixed-vlmax-1.c.

gcc/ChangeLog:

	* config/riscv/autovec.md (movmisalign<mode>): New pattern.
	* config/riscv/riscv-protos.h (riscv_vector_mask_mode_p): Delete.
	(riscv_vector_get_mask_mode): Ditto.
	(get_mask_policy_no_pred): Ditto.
	(get_tail_policy_no_pred): Ditto.
	(get_mask_mode): New function.
	* config/riscv/riscv-v.cc (get_mask_policy_no_pred): Delete.
	(get_tail_policy_no_pred): Ditto.
	(riscv_vector_mask_mode_p): Ditto.
	(riscv_vector_get_mask_mode): Ditto.
	(get_mask_mode): New function.
	* config/riscv/riscv-vector-builtins.cc (use_real_merge_p): Remove
	global extern.
	(get_tail_policy_for_pred): Ditto.
	* config/riscv/riscv-vector-builtins.h (get_tail_policy_for_pred): Ditto.
	(get_mask_policy_for_pred): Ditto
	* config/riscv/riscv.cc (riscv_get_mask_mode): Refine codes.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/fixed-vlmax-1.c: Fix typo.