Enable EGPR for `GenTree` nodes that lower to promoted VEX/EVEX encoding.

[anthonycanino]

#113237 completed EGPR for VEX/EVEX encoding. Prior to that, some GenTree nodes that would have required this support were masked off from using the EGPRs in the register allocator.

This task is to remove the limitation.

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.