[SVE] Restrict the usage of REINTERPRET_CAST.

In order to limit the number of combinations of REINTERPRET_CAST,
whilst at the same time prevent overlap with BITCAST, this patch
establishes the following rules:

1. The operand and result element types must be the same.
2. The operand and/or result type must be an unpacked type.

Differential Revision: https://reviews.llvm.org/D94593