Include platsmp.h for the definition of bcm2836_smp_ops to fix
the following warning:

arch/arm/mach-bcm/platsmp.c:334:29: warning: symbol 'bcm2836_smp_ops' was not declared. Should it be static?
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Acked-by: Scott Branden <scott.branden@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>