ARM: 9315/1: fiq: include asm/mach/irq.h for prototypes

There are two global functions in fiq.c that get called from
other files through an extern declaration, but a W=1 build
warns about the header not being included before the definition:

arch/arm/kernel/fiq.c:85:5: error: no previous prototype for 'show_fiq_list' [-Werror=missing-prototypes]
arch/arm/kernel/fiq.c:159:13: error: no previous prototype for 'init_FIQ' [-Werror=missing-prototypes]

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>