Bring back escape valve for llm libraries and fix Jetpack6 crash (#12529)

* Bring back escape valve for llm libraries

If the new discovery logic picks the wrong library, this gives users the
ability to force a specific one using the same pattern as before. This
can also potentially speed up bootstrap discovery if one of the libraries
takes a long time to load and ultimately bind to no devices.  For example
unsupported AMD iGPUS can sometimes take a while to discover and rule out.

* Bypass extra discovery on jetpack systems

On at least Jetpack6, cuda_v12 appears to expose the iGPU, but crashes later on in
cublasInit so if we detect a Jetpack, short-circuit and use that variant.

discover/gpu.go

@@ -6,7 +6,9 @@ import (
 	"log/slog"
 	"os"
 	"path/filepath"
+	"regexp"
 	"runtime"
+	"strconv"
 	"strings"
 
 	"github.com/ollama/ollama/format"
@@ -146,3 +148,35 @@ func GetSystemInfo() SystemInfo {
 		GPUs: gpus,
 	}
 }
+
+func cudaJetpack() string {
+	if runtime.GOARCH == "arm64" && runtime.GOOS == "linux" {
+		if CudaTegra != "" {
+			ver := strings.Split(CudaTegra, ".")
+			if len(ver) > 0 {
+				return "jetpack" + ver[0]
+			}
+		} else if data, err := os.ReadFile("/etc/nv_tegra_release"); err == nil {
+			r := regexp.MustCompile(` R(\d+) `)
+			m := r.FindSubmatch(data)
+			if len(m) != 2 {
+				slog.Info("Unexpected format for /etc/nv_tegra_release.  Set JETSON_JETPACK to select version")
+			} else {
+				if l4t, err := strconv.Atoi(string(m[1])); err == nil {
+					// Note: mapping from L4t -> JP is inconsistent (can't just subtract 30)
+					// https://developer.nvidia.com/embedded/jetpack-archive
+					switch l4t {
+					case 35:
+						return "jetpack5"
+					case 36:
+						return "jetpack6"
+					default:
+						// Newer Jetson systems use the SBSU runtime
+						slog.Debug("unrecognized L4T version", "nv_tegra_release", string(data))
+					}
+				}
+			}
+		}
+	}
+	return ""
+}