Half of the threads fail with RX470 and AstroBWT
When starting a rig with 3 x RX470's I get the errors listed below, these threads fail to mine while the rest work just fine.

```
error CL_MEM_OBJECT_ALLOCATION_FAILURE when calling clEnqueueWriteBuffer
thread #4 failed with error CL_MEM_OBJECT_ALLOCATION_FAILURE
error CL_MEM_OBJECT_ALLOCATION_FAILURE when calling clEnqueueWriteBuffer
thread #0 failed with error CL_MEM_OBJECT_ALLOCATION_FAILURE
error CL_MEM_OBJECT_ALLOCATION_FAILURE when calling clEnqueueWriteBuffer
thread #2 failed with error CL_MEM_OBJECT_ALLOCATION_FAILURE
```

Screenshot -> https://ibb.co/XVQxLQr

I've tried to dig around and it seems that these errors can be due to the wrong intensity settings, but I then ran into 2 major problems trying to fix it :

1) I can't find any information on how to set intensity levels in the official docs

2) The user submitted info I could find relative to intensity settings was all for Monero (and years old at that) - there is virtually nothing about AstroBWT out there.

I'm using xmrig 6.5.13

I'm using the latest AMD drivers (as of the date of this post) and all cards are running on their factory bios.

I'm starting xmrig using a .bat file (not using the config file)
