Various fixes + cleanup.

- Add parts.rst documentation for Linux kernel.
- Completely fix problems caused by new bootstrap, update checksums for
  /usr.
- Globalise populate_device_nodes.
- Enable deblobbing.

sysc/pkg-config-0.29.2/checksums

@@ -0,0 +1 @@
+f92d3a73adae8cef9d016f665bf825411b07f5b258ae607237fadc320d6b52f1  /usr/bin/pkg-config

sysc/pkg-config-0.29.2/pkg-config-0.29.2.sh

@@ -0,0 +1,16 @@
+# SPDX-FileCopyrightText: 2021 Andrius Štikonas <andrius@stikonas.eu>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+src_prepare() {
+    autoreconf -fi
+}
+
+src_configure() {
+    # We use internal glib because standalone glib library depends on
+    # pkg-config and other software (python/meson) that we do not have.
+    ./configure \
+        --prefix="${PREFIX}" \
+        --build=i386-unknown-linux-musl \
+        --with-internal-glib
+}