Regression from fix: older GPUs show x2-x3 slowdown

[Nashatyrev]

https://github.com/KlausT/ccminer-cryptonight/commit/824db322bb7f0dad920711ca29dbe1457ff79f49 This fix makes some older (or just some mobile only) GPU perform 2x-3x slower with default settings. Reproduced on 840M and 960M 840M (3 smx):

• before the fix: 12 blocks of 8 threads: 66H/s
• after the fix: 12 blocks of 32 threads: 25H/s

[Nashatyrev]

Sorry this was not only the mentioned commit but all the changes to default auto config starting from https://github.com/KlausT/ccminer-cryptonight/commit/b4d0f509b4ef5cf9c86f85180cf31dfb6e29a9f2