eliminateFrameIndex wasn't handling the FI copy to Scalar registers and
the default implementation breaks the code while trying to handle it.
This patch handles the broken lowering and also takes care of some edge
cases that might arise. This case is tricky for non-zero offset, scc &
vcc is live and we don't find sgpr pair available.
Co-authored by @arsenm
---------
Co-authored-by: Matt Arsenault <Matthew.Arsenault@amd.com>
Co-authored-by: PankajDwivedi-25 <pankajkumar.divedi@amd.com>
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