Revamp ROCm support

This refines where we extract the LLM libraries to by adding a new
OLLAMA_HOME env var, that defaults to `~/.ollama` The logic was already
idempotenent, so this should speed up startups after the first time a
new release is deployed.  It also cleans up after itself.

We now build only a single ROCm version (latest major) on both windows
and linux.  Given the large size of ROCms tensor files, we split the
dependency out.  It's bundled into the installer on windows, and a
separate download on windows.  The linux install script is now smart and
detects the presence of AMD GPUs and looks to see if rocm v6 is already
present, and if not, then downloads our dependency tar file.

For Linux discovery, we now use sysfs and check each GPU against what
ROCm supports so we can degrade to CPU gracefully instead of having
llama.cpp+rocm assert/crash on us.  For Windows, we now use go's windows
dynamic library loading logic to access the amdhip64.dll APIs to query
the GPU information.

docs/troubleshooting.md

@@ -67,6 +67,43 @@ You can see what features your CPU has with the following.
 cat /proc/cpuinfo| grep flags  | head -1
 ```
 
+## AMD Radeon GPU Support
+
+Ollama leverages the AMD ROCm library, which does not support all AMD GPUs. In
+some cases you can force the system to try to use a close GPU type.  For example
+The Radeon RX 5400 is `gfx1034` (also known as 10.3.4) however, ROCm does not
+support this patch-level, the closest support is `gfx1030`.  You can use the
+environment variable `HSA_OVERRIDE_GFX_VERSION` with `x.y.z` syntax.  So for
+example, to force the system to run on the RX 5400, you would set
+`HSA_OVERRIDE_GFX_VERSION="10.3.0"` as an environment variable for the server.
+
+At this time, the known supported GPU types are the following: (This may change from
+release to release)
+- gfx900
+- gfx906
+- gfx908
+- gfx90a
+- gfx940
+- gfx941
+- gfx942
+- gfx1030
+- gfx1100
+- gfx1101
+- gfx1102
+
+This will not work for all unsupported GPUs.  Reach out on [Discord](https://discord.gg/ollama)
+or file an [issue](https://github.com/ollama/ollama/issues) for additional help.
+
+
+## Installing older versions on Linux
+
+If you run into problems on Linux and want to install an older version you can tell the install script
+which version to install.
+
+```sh
+curl -fsSL https://ollama.com/install.sh | OLLAMA_VERSION="0.1.27" sh
+```
+
 ## Known issues
 
 * N/A