powerpc: Respect nr_cpu_ids when calling set_cpu_possible and set_cpu_present

We should not set cpus above nr_cpu_ids to possible.  While we
will trigger a warning with CONFIG_CPUMASK_DEBUG, even then the mask
initializers will set the bits beyond what the iterators check and cause
nr_cpu_ids to increase.

Respecting nr_cpu_ids during setup will allow us to use it in our initial
paca allocation.  It can be reduced from NR_CPUS by the existing early param
nr_cpus=, which was added in 2b633e3f (smp:
Use nr_cpus= to set nr_cpu_ids early).  We already call parse_early_parms
between finding the command line and allocating the pacas.

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>