aarch64: Support permutes on unpacked SVE vectors

This patch adds support for permuting unpacked SVE vectors using:

- DUP
- EXT
- REV[BHW]
- REV
- TRN[12]
- UZP[12]
- ZIP[12]

This involves rewriting the REV[BHW] permute code so that the inputs
and outputs of the insn pattern have the same mode as the vectors
being permuted.  This is different from the ACLE form, where the
reversal happens within individual elements rather than within
groups of multiple elements.

The patch does not add a conditional version of REV[BHW].  I'll come
back to that once we have partial-vector comparisons and selects.

The patch is really just enablement, adding an extra tool to the
toolbox.  It doesn't bring any significant vectorisation opportunities
on its own.  However, the patch does have one artificial example that
is now vectorised in a better way than before.

gcc/
	* config/aarch64/aarch64-modes.def (VNx2BF, VNx4BF): Adjust nunits
	and alignment based on the current VG.
	* config/aarch64/iterators.md (SVE_ALL, SVE_24, SVE_2, SVE_4): Add
	partial SVE BF modes.
	(UNSPEC_REVBHW): New unspec.
	(Vetype, Vesize, Vctype, VEL, Vel, vwcore, V_INT_CONTAINER)
	(v_int_container, VPRED, vpred): Handle partial SVE BF modes.
	(container_bits, Vcwtype): New mode attributes.
	* config/aarch64/aarch64-sve.md
	(@aarch64_sve_revbhw_<SVE_ALL:mode><PRED_HSD:mode>): New pattern.
	(@aarch64_sve_dup_lane<mode>): Extended from SVE_FULL to SVE_ALL.
	(@aarch64_sve_rev<mode>, @aarch64_sve_<perm_insn><mode>): Likewise.
	(@aarch64_sve_ext<mode>): Likewise.
	* config/aarch64/aarch64.c (aarch64_classify_vector_mode): Handle
	E_VNx2BFmode and E_VNx4BFmode.
	(aarch64_evpc_rev_local): Base the analysis on the container size
	instead of the element size.  Use the new aarch64_sve_revbhw
	patterns for SVE.
	(aarch64_evpc_dup): Handle partial SVE data modes.  Use the
	container size instead of the element size when applying the
	SVE immediate limit.  Fix a previously incorrect bounds check.
	(aarch64_expand_vec_perm_const_1): Handle partial SVE data modes.

gcc/testsuite/
	* gcc.target/aarch64/sve/dup_lane_2.c: New test.
	* gcc.target/aarch64/sve/dup_lane_3.c: Likewise.
	* gcc.target/aarch64/sve/ext_4.c: Likewise.
	* gcc.target/aarch64/sve/rev_2.c: Likewise.
	* gcc.target/aarch64/sve/revhw_1.c: Likewise.
	* gcc.target/aarch64/sve/revhw_2.c: Likewise.
	* gcc.target/aarch64/sve/slp_perm_8.c: Likewise.
	* gcc.target/aarch64/sve/trn1_2.c: Likewise.
	* gcc.target/aarch64/sve/trn2_2.c: Likewise.
	* gcc.target/aarch64/sve/uzp1_2.c: Likewise.
	* gcc.target/aarch64/sve/uzp2_2.c: Likewise.
	* gcc.target/aarch64/sve/zip1_2.c: Likewise.
	* gcc.target/aarch64/sve/zip2_2.c: Likewise.