AMD Vega64 CN-GPU low auto intensity.

[Ryo-RU]

TLDR: When started V56 xmr-stak generates proper intensity in config. But V64 - not.
Algo: CN-GPU
Tested on 2 different devices on HiveOS and W10
[Imgur link]

Details:
This seem to appear on 2.10.7 (2.10.5 generates 1536 auto-intensity)
Auto intensity: 1024 (the rest is fine: worksize 16, memchunk 2, 1 thread)
Manually found that intensity 2016 is the best spot there.

(2023 / (16*64) * 64*16 = 1024 for Vega 64
(2023/ (16*56)) * 56*16 = 1792 for Vega 56

Bcs of 1,9 turning into 1 here = 64*16 gives 1024 as a result.

Both have same GPU codename: gfx900

4024/2 = threads = 2012
(2012 / 16)) * 16 = 2000
Ending with at least 2000 intensity in one thread with ws16 will be optimal with extra reserve space to prevent possible crashes.

Thanks to Villos1 (HiveOS team) and newtoetn from discord for feedback

[psychocrypt]

fixed in #2518