MAINTAINERS: Add entry for debug objects

This is overdue and an oversight.

Add myself to this file deespite the fact that I'm trying to reduce the
number of entries in this file which have my name attached, but in the
hope that patches wont get picked up elsewhere completely unreviewed and
unnoticed.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>