x86/uv: fix init of cpu-less nodes

Fix an endcase in the UV initialization code for the "UV large system mode"
of apicids.  If node zero contains no cpus, cpus on another node will be the
boot cpu.  The percpu data that contains the extra apicid bits was not
being initialized early enough.

[ Impact: fix potential boot crash on cpu-less UV nodes ]

Signed-off-by: Jack Steiner <steiner@sgi.com>
LKML-Reference: <20090417142447.GA23759@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>