Dave Baumann categorically stated that OpenCL2.0 is a GCN1.1(what he calls GCN2) and above thing only.
What performance improvements it might have over GCN1.0 is up for debate and I haven't looked into those.
The recent M370X in macbooks was deemed a Cape Verde GCN1.0 rebrand but it basically obliterates the previous supposedly GCN1.0 rebrand(or GCN1.1 rebrand?) in the games where Tonga does the best against Tahiti.
Interestingly, here's a table of some of the GCN gpus, see how Topaz which has been branded a rebrand just like the previous mobile chips has an updated IP compared to Hawaii(which is undoubtedly GCN1.1) and has a memory controller on par with Tonga.