init.rc: restorecon_recursive /sys/kernel/debug

If /sys/kernel/debug is present, make sure it has all the appropriate
SELinux labels.

Labeling of /sys/kernel/debug depends on kernel support
added in commit https://android-review.googlesource.com/122130

This patch depends on an external/sepolicy change with the
same Change-Id as this patch.

Change-Id: Id1d6a9ad6d0759d6de839458890e8cb24685db6d