irqchip/mxs: Include linux/irqchip/mxs.h

This header contains the definition for icoll_handle_irq(), which
is used in arch/arm/mach-mxs/mach-mxs.c, without this we get a warning
about a missing prototype when building with W=1.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230516200516.554663-4-arnd@kernel.org