[PATCH] kernel.h: Include <linux/bug.h> to avoid build breakage with ARRAY_SIZE()

    arch/arm/mach-ux500/reboot_reasons.c:26:1: error: implicit declaration of function 'BUILD_BUG_ON_ZERO' [-Werror=implicit-function-declaration]
    arch/arm/mach-ux500/reboot_reasons.c:26:1: error: initializer element is not constant

    commit 6f863554 (kernel.h: doesn't explicitly use bug.h, so don't include it.)
    has removed asm/debug.h from linux/kernel.h.

    Quoting Russell King (http://www.spinics.net/lists/arm-kernel/msg161916.html)

    "linux/kernel.h _does_ use bug stuff - in ARRAY_SIZE().

    ARRAY_SIZE() uses __must_be_array(), which is defined in linux/compiler-gcc.h,
    which is obtained via linux/compiler.h and linux/linkage.h.

    linux/compiler-gcc.h defines __must_be_array() to be:
    #define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))

    and BUILD_BUG_ON_ZERO used to be in linux/kernel.h but got moved to linux/bug.h.

    Hence why people are seeing build breakage with ARRAY_SIZE()."

    Signed-off-by: Fabio Estevam <fabio.estevam@xxxxxxxxxxxxx>