[MachineCopyPropagation] Eliminate spillage copies that might be caused by eviction chain

Remove spill-reload like copy chains. For example
```
r0 = COPY r1
r1 = COPY r2
r2 = COPY r3
r3 = COPY r4
<def-use r4>
r4 = COPY r3
r3 = COPY r2
r2 = COPY r1
r1 = COPY r0
```
will be folded into
```
r0 = COPY r1
r1 = COPY r4
<def-use r4>
r4 = COPY r1
r1 = COPY r0
```

Reviewed By: qcolombet

Differential Revision: https://reviews.llvm.org/D122118