ARM: 6881/1: cputype.h uses __attribute_const__ which requires including kernel.h

Issue manifests as:

In file included from arch/arm/mach-pxa/include/mach/hardware.h:62,
from arch/arm/mach-pxa/include/mach/gpio.h:28,
from /home/jic23/src/kernel/temp-remove/arch/arm/include/asm/gpio.h:5,
from include/linux/gpio.h:7,
from drivers/staging/iio/gyro/adis16080_core.c:8:
/home/jic23/src/kernel/temp-remove/arch/arm/include/asm/cputype.h:57: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'read_cpuid_id'
...

Signed-off-by: Jonathan Cameron <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

arch/arm/include/asm/cputype.h

···
 #define __ASM_ARM_CPUTYPE_H
 
 #include <linux/stringify.h>
+#include <linux/kernel.h>
 
 #define CPUID_ID	0
 #define CPUID_CACHETYPE	1