CRISv32: Add missing include for mm.h

Fixes the following compile error.

arch/cris/arch-v32/kernel/time.c: In function 'reset_watchdog':
arch/cris/arch-v32/kernel/time.c:121:2:
        error: implicit declaration of function 'global_page_state'

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Jesper Nilsson <jesper.nilsson@axis.com>