suppress modprobe errors on builtins (credits to Kay Sievers)

Install /lib/modules/$kv/modules.builtin.bin to suppress modprobe error
messages saying module was not found, while it's built-in.

Credits go to Kay Sievers who enlighten us about meaning of this cool
file.

modules.d/90kernel-modules/install

@@ -4,3 +4,4 @@
 [ -f /etc/modprobe.conf ] && dracut_install /etc/modprobe.conf
 dracut_install $(find /etc/modprobe.d/ -type f -name '*.conf')
 inst_hook cmdline 01 "$moddir/parse-kernel.sh"
+inst "$srcmods/modules.builtin.bin"