[AArch64][SME2] Allow lowering to whilelo.x2 in non-streaming mode (#178399)
Since #145322 relaxed the SME predicate for the multi-register while
instructions, these instructions are allowed in non-streaming mode
when SME2 is available.
This patch removes the isStreaming() restriction from both
performActiveLaneMaskCombine & ReplaceGetActiveLaneMaskResults,
allowing the whilelo.x2 intrinsic to be used if SVE or streaming
SVE is available.