[AArch64] Add worst case shuffle costs

[AArch64] Add worst case shuffle costs

This adds some missing single source shuffle costs for AArch64, of i16
and i8 vectors. v4i16 are the same as v4i32 with a worse case cost of 3
coming from the perfect shuffle tables. The larger vector sizes expand
into a constant pool, plus a load (and adrp) and a tbl. I arbitrarily
chose 8 for the cost to be expensive but not too expensive.

Differential Revision: https://reviews.llvm.org/D106241