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

This reverts commit 5b7e5676.

Although including linux/irqchip/mxs.h is technically correct,
this clashes with the parallel removal of this include file
with 32bit ARM modernizing the low level irq handling as part of
5bb578a0 ("ARM: 9298/1: Drop custom mdesc->handle_irq()").

As such, this patch is not only unnecessary, it also breaks
compilation in -next. Revert it.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Shawn Guo <shawnguo@kernel.org>