ARM: 8371/1: always select IRQ_WORK on SMP

Any SMP kernel now requires the irq_work code after
generic_smp_call_function_single_interrupt() started using it,
or we get:

kernel/built-in.o: In function `flush_smp_call_function_queue':
:(.text+0x4dc3a): undefined reference to `irq_work_run'

Fixes: 47885016 ("irq_work: Implement remote queueing")

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>