Wrap long lines
[AVX512] Pull everything alignr-related into the multiclass

The packed integer pattern becomes the DAG pattern for rri and the packed
float, another Pat<> inside the multiclass.

No functional change.
[AVX512] alignr: Use suffix rather than name argument to multiclass

Again no functional change.  This prepares for the suffix to be used with the
intrinsic matching.
[X86] Separate DAG node for valign and palignr

They have different semantics (valign is interlane while palingr is intralane)
and palingr is still needed even in the AVX512 context.  According to the
latest spec AVX512BW provides these.
[X86] Add lowering to VALIGN

This was currently part of lowering to PALIGNR with some special-casing to
make interlane shifting work.  Since AVX512F has interlane alignr (valignd/q)
and AVX512BW has vpalignr we need to support both of these *at the same time*,
e.g. for SKX.

This patch breaks out the common code and then add support to check both of
these lowering options from LowerVECTOR_SHUFFLE.

I also added some FIXMEs where I think the AVX512BW and AVX512VL additions
should probably go.
[X86] Increase X86_MAX_OPERANDS from 5 to 6

This controls the number of operands in the disassembler's x86OperandSets
table.  The entries describe how the operand is encoded and its type.

Not to surprisingly 5 operands is insufficient for AVX512.  Consider
VALIGNDrrik in the next patch.  These are its operand specifiers:

  { /* 328 */
    { ENCODING_DUP, TYPE_DUP1 },
    { ENCODING_REG, TYPE_XMM512 },
    { ENCODING_WRITEMASK, TYPE_VK8 },
    { ENCODING_VVVV, TYPE_XMM512 },
    { ENCODING_RM_CD64, TYPE_XMM512 },
    { ENCODING_IB, TYPE_IMM8 },
  },
[AVX512] Add masking variant and intrinsics for valignd/q

This is similar to what I did with the two-source permutation recently.  (It's
almost too similar so that we should consider generating the masking variants
with some tablegen help.)

Both encoding and intrinsic tests are added as well.  For the latter, this is
what the IR that the intrinsic test on the clang side generates.

Part of <rdar://problem/17688758>