MAINTAINERS: Add myself as scheduler topology reviewer

I've messed around the NUMA/debug bits of the scheduler toplogy in my
time at Arm, and even though I've changed ships I still intend to at the
very least review those bits.

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220406141315.732473-2-vschneid@redhat.com