[AArch64][SME] Add coalescer barrier for args/results in locally streaming functions. (#85388)

Similar to how we protected FP/fixed-vector arguments and results from
calls, we should do the same for arguments/results from locally-streaming
functions such that those are not spilled/filled as ZPR registers.

This may cause a small regression (additional spills/fills), which is
addressed by #85386.