aarch64: Refactor TBL/TBX RTL patterns

Rename two-source-register TBL/TBX RTL patterns so that their names
better reflect what they do, rather than confusing them with tbl3 or
tbx4 patterns. Also use the correct "neon_tbl2" type attribute for
both patterns.

Rename single-source-register TBL/TBX patterns for consistency.

gcc/ChangeLog:

2021-07-08  Jonathan Wright  <jonathan.wright@arm.com>

	* config/aarch64/aarch64-simd-builtins.def: Use two variant
	generators for all TBL/TBX intrinsics and rename to
	consistent forms: qtbl[1234] or qtbx[1234].
	* config/aarch64/aarch64-simd.md (aarch64_tbl1<mode>):
	Rename to...
	(aarch64_qtbl1<mode>): This.
	(aarch64_tbx1<mode>): Rename to...
	(aarch64_qtbx1<mode>): This.
	(aarch64_tbl2v16qi): Delete.
	(aarch64_tbl3<mode>): Rename to...
	(aarch64_qtbl2<mode>): This.
	(aarch64_tbx4<mode>): Rename to...
	(aarch64_qtbx2<mode>): This.
	* config/aarch64/aarch64.c (aarch64_expand_vec_perm_1): Use
	renamed qtbl1 and qtbl2 RTL patterns.
	* config/aarch64/arm_neon.h (vqtbl1_p8): Use renamed qtbl1
	RTL pattern.
	(vqtbl1_s8): Likewise.
	(vqtbl1_u8): Likewise.
	(vqtbl1q_p8): Likewise.
	(vqtbl1q_s8): Likewise.
	(vqtbl1q_u8): Likewise.
	(vqtbx1_s8): Use renamed qtbx1 RTL pattern.
	(vqtbx1_u8): Likewise.
	(vqtbx1_p8): Likewise.
	(vqtbx1q_s8): Likewise.
	(vqtbx1q_u8): Likewise.
	(vqtbx1q_p8): Likewise.
	(vtbl1_s8): Use renamed qtbl1 RTL pattern.
	(vtbl1_u8): Likewise.
	(vtbl1_p8): Likewise.
	(vtbl2_s8): Likewise
	(vtbl2_u8): Likewise.
	(vtbl2_p8): Likewise.
	(vtbl3_s8): Use renamed qtbl2 RTL pattern.
	(vtbl3_u8): Likewise.
	(vtbl3_p8): Likewise.
	(vtbl4_s8): Likewise.
	(vtbl4_u8): Likewise.
	(vtbl4_p8): Likewise.
	(vtbx2_s8): Use renamed qtbx2 RTL pattern.
	(vtbx2_u8): Likewise.
	(vtbx2_p8): Likewise.
	(vqtbl2_s8): Use renamed qtbl2 RTL pattern.
	(vqtbl2_u8): Likewise.
	(vqtbl2_p8): Likewise.
	(vqtbl2q_s8): Likewise.
	(vqtbl2q_u8): Likewise.
	(vqtbl2q_p8): Likewise.
	(vqtbx2_s8): Use renamed qtbx2 RTL pattern.
	(vqtbx2_u8): Likewise.
	(vqtbx2_p8): Likewise.
	(vqtbx2q_s8): Likewise.
	(vqtbx2q_u8): Likewise.
	(vqtbx2q_p8): Likewise.
	(vtbx4_s8): Likewise.
	(vtbx4_u8): Likewise.
	(vtbx4_p8): Likewise.