irqchip: add to the directories part of the IRQ subsystem in MAINTAINERS

Now that the drivers/irqchip/ directory is getting more code, it needs
a maintainer. The obvious maintainer for it is Thomas Gleixner, who is
maintaining the overall IRQ subsystem. So we add drivers/irqchip/ in
the list of directories that are part of the IRQ subsystem.
Signed-off-by: NThomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: NRob Herring <rob.herring@calxeda.com>

MAINTAINERS

@@ -4209,6 +4209,7 @@ M:	Thomas Gleixner <tglx@linutronix.de>
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git irq/core
 F:	kernel/irq/
+F:	drivers/irqchip/
 
 IRQ DOMAINS (IRQ NUMBER MAPPING LIBRARY)
 M:	Benjamin Herrenschmidt <benh@kernel.crashing.org>