Enable RegDepCopyRemoval on Z

[fjeremic]

See #12188. We should investigate whether this is beneficial on Z and enable it if deemed so.

[r30shah]

I remember having discussions about this with Andrew last year when working on to fix some issues with this Opt and PostGRA Block splitter. At that time while evaluating, on x86 this optimization gave me 0.3-0.4% improvement on Liberty-DayTrader with Java8.
One of the potential reason, we are getting something out of this optimization on x86 more is because the less number of Global Registers available on x86 causing more register spilling which could not be the case for Z where we have more Global Registers available.

[fjeremic]

@0xdaryl FYI on above. Not sure if AArch64 has similar issues. It may not be worth the investment if AArch64 falls in the same bucket as Z w.r.t. global register usage.