Radeon VII CN-GPU auto config optimisation

[Ryo-RU]

same problem we had with Vega in Cn-GPU applies to VII.
Stock config has WS of 8 with 1600hs, when set to 16 - hash increases to expected values (2000hs).

["gpu_threads_conf" : [
  // gpu: gfx906  compute units: 60
  // memory:4048|4048|16064 MiB (used per thread|max per alloc|total free)
  { "index" : 0,
    "intensity" : 1920, "worksize" : 16,
    "affine_to_cpu" : false, "strided_index" : 0, "mem_chunk" : 2,
    "unroll" : 1, "comp_mode" : true, "interleave" : 40
  },
],]

HASHRATE REPORT - AMD
| ID | 10s | 60s | 15m |
| 0 | 2055.2 | 2095.9 | (na) |

[psychocrypt]

fixed with #2520