Include linked firmware files

Some modules reference a firmware file that is just a link to a "real"
file. Make sure those files are also included when needed by resolving
those referenced symlinks and including their target files in the set of
required firmware files.

mkosi/kmod.py

@@ -180,6 +180,11 @@ def gen_required_kernel_modules(
             mods = set(modulesd.rglob("*.ko*"))
         firmware = set()
 
+    links = {
+        p.resolve().relative_to(root)
+        for p in filter(lambda fw: fw.is_symlink() and fw.exists(), map(lambda fw: root / fw, firmware))
+    }
+
     yield from sorted(
         itertools.chain(
             {
@@ -189,6 +194,7 @@ def gen_required_kernel_modules(
             },
             mods,
             firmware,
+            links,
             (p.relative_to(root) for p in (root / modulesd).glob("modules*")),
         )
     )