[AArch64][SVE] Improve diagnostics for vectors with incorrect element-size.

[AArch64][SVE] Improve diagnostics for vectors with incorrect element-size.

For regular SVE vector operands, this patch introduces a more
sensible diagnostic when the vector has a wrong suffix (e.g. z0.s vs z0.b).

For example:
  add z0.s, z1.s, z2.b      -> invalid element width
               ^_____^
               mismatch

For the vector-with-shift/extend (e.g. z0.s, uxtw #2) this patch takes
a slightly different approach and instead returns a 'invalid operand'
if the element size is not as expected. This is because the diagnostics
are more specificied to suggest using the right shift/extend suffix. This
is a trade-off not to introduce more operand classes and still provide
useful diagnostics for LD1 and PRF instructions.

For example:
  ld1w z1.s, p0/z, [x0, z0.s] -> invalid shift/extend specified, expected 'z[0..31].s, (uxtw|sxtw)'
  ld1w z1.d, p0/z, [x0, z0.s] -> invalid operand
          ^________________^
               mismatch

For gather prefetches, both 'z0.s' and 'z0.d' would be allowed:
  prfw #0, p0, [x0, z0.s]   -> invalid shift/extend specified, expected 'z[0..31].s, (uxtw|sxtw) #2'
  prfw #0, p0, [x0, z0.d]   -> invalid shift/extend specified, expected 'z[0..31].d, (lsl|uxtw|sxtw) #2'

Without this change, the diagnostic would unnecessarily suggest a
different element size:
  prfw #0, p0, [x0, z0.s]   -> invalid shift/extend specified, expected 'z[0..31].d, (lsl|uxtw|sxtw) #2'

Reviewers: SjoerdMeijer, aemerson, fhahn, samparker, javed.absar

Reviewed By: SjoerdMeijer

Differential Revision: https://reviews.llvm.org/D46688

llvm-svn: 332483