[X86] AMD Zen 3: 32/64 -bit GPR register moves are zero-cycle

I've verified this with llvm-exegesis.
This is not limited to zero registers.

Refs:
AMD SOG 19h, 2.9.4 Zero Cycle Move
The processor is able to execute certain register to register
mov operations with zero cycle delay.

Agner,
22.13 Instructions with no latency
Register-to-register move instructions are resolved at
the register rename stage without using any execution units.
These instructions have zero latency. It is possible to do six such
register renamings per clock cycle, and it is even possible to
rename the same register multiple times in one clock cycle.