MAINTAINERS: Add co-maintainers for time[rs]

Anna-Maria and Frederic are working in this area for years. Volunteer them
into co-maintainer roles.

While at it bring the file lists up to date.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20240325172048.548199937@linutronix.de