move all our stuff into /lkmc in guest

Motivation: userland is getting several new subdirectories, it would be
too insane to just dump all of that in the guest root filesystem.

To alleviate the cd pain, .profile puts user inside /lkmc by default.

rootfs_overlay/lkmc/sysfs.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+set -e
+insmod sysfs.ko
+f=/sys/kernel/lkmc_sysfs/foo
+# write
+printf 12345 > "$f"
+# read
+[ "$(cat "$f")" = 1234 ]
+# seek
+[ "$(dd if="$f" bs=1 count=2 skip=1 status=none)" = 23 ]
+rmmod sysfs