ARM: 7586/1: sp804: set cpumask to cpu_possible_mask for clock event device

The SP804 driver statically initialises the cpumask of the clock event
device to be cpu_all_mask, which is derived from the compile-time
constant NR_CPUS. This breaks SMP_ON_UP systems where the interrupt
controller handling the sp804 doesn't have the irq_set_affinity callback
on the irq_chip, because the common timer code fails to identify the
device as cpu-local and ends up treating it as a broadcast device
instead.

This patch fixes the problem by using cpu_possible_mask at runtime,
which will correctly represent the possible CPUs when SMP_ON_UP is being
used.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>