MAINTAINERS: Add myself as context tracking maintainer

I've been missing a lot of patches touching context tracking for which
I wasn't Cc'ed these last months. The code looks like a simple single
file but has a lot of subtle tentacles.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210512232924.150322-11-frederic@kernel.org

MAINTAINERS

@@ -4601,6 +4601,12 @@ S:	Supported
 F:	drivers/video/console/
 F:	include/linux/console*
 
+CONTEXT TRACKING
+M:	Frederic Weisbecker <frederic@kernel.org>
+S:	Maintained
+F:	kernel/context_tracking.c
+F:	include/linux/context_tracking*
+
 CONTROL GROUP (CGROUP)
 M:	Tejun Heo <tj@kernel.org>
 M:	Zefan Li <lizefan.x@bytedance.com>