[IA64] Fix build breakage

[IA64] Fix build breakage

In commit 5a145240110ce8315fa8a2a1e455df7e32e60c4f
cpusets: randomize node rotor used in cpuset_mem_spread_node()

Jack Steiner fixed a problem with too many small tasks being
assigned to node 0. Copy his code to ia64 to avoid build error.

    arch/ia64/kernel/smpboot.c:641: error: ‘cpu_to_node_map’ undeclared (first use in this function)

In commit d9bf32d2ae4be422114f00bbde53e02f177291f4
numa: ia64: use generic percpu var numa_node_id() implementation

Lee Schermerhorn added some set_numa_node() calls - but these
only work on CONFIG_NUMA=y configurations. Surround the calls
with #ifdef CONFIG_NUMA

Signed-off-by: Tony Luck <tony.luck@intel.com>