ARM: fix rcu stalls on SMP platforms

We can stall RCU processing on SMP platforms if a CPU sits in its idle
loop for a long time.  This happens because we don't call irq_enter()
and irq_exit() around generic_smp_call_function_interrupt() and
friends.  Add the necessary calls, and remove the one from within
ipi_timer(), so that they're all in a common place.

Change-Id: I18aba9978f1a3497d8a960f2f9e3618248eb0107
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Joel King <joelking@codeaurora.org>
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>