cpumask: Avoid cpumask_t in arch/x86/kernel/apic/nmi.c

Ingo wants the certainty of a static cpumask (rather than a
cpumask_var_t), but cpumask_t will some day be undefined to
avoid on-stack declarations.

This is what DECLARE_BITMAP/to_cpumask() is for.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
LKML-Reference: <200911031453.52394.rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>