MAINTAINERS: Remove myself from the general IRQ subsystem maintenance

It is pretty obvious that I haven't done much on the IRQ side
for a while, and it is unlikely that I'll have more bandwidth
for it any time soon. People keep sending me patches that
I end-up reviewing in a cursory manner, which isn't great for
anyone.

So in everyone's interest, I'm removing myself from the list
of maintainers and leave the irqchip and irqdomain subsystems
in Thomas' capable hands.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231002141302.3409485-3-maz@kernel.org