[MachineFrameInfo][RISCV] Call ensureStackAlignment for objects created with scalable...

[MachineFrameInfo][RISCV] Call ensureStackAlignment for objects created with scalable vector stack id.

This is an alternative to fix PR57939 for RISC-V. It definitely
can be argued that the stack temporaries for RISC-V are being created
with an unnecessarily large alignment. But ignoring the alignment
in MachineFrameInfo also seems bad.

Looking at the test update that go with the current ID==0 check,
it was intending to exclude things like the NoAlloc stackid. So I'm
not sure if scalable vectors are intentionally being excluded.

Reviewed By: reames

Differential Revision: https://reviews.llvm.org/D135913