models: Move model into their own directory

This allows there to be a file that is a list of models that is
not mixed into the runner code.

model/models/models.go

@@ -0,0 +1,6 @@
+package models
+
+import (
+	_ "github.com/ollama/ollama/model/models/llama"
+	_ "github.com/ollama/ollama/model/models/mllama"
+)