ARM: 5945/1: ep93xx: include correct irq.h in core.c

Currently <asm/mach/irq.h> is included by core.c. This header
includes <linux/irq.h> and defines a number of internal functions.
These internal functions are not needed by this file. Change the
include so that we just get what is needed.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Ryan Mallon <ryan@bluewatersys.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>