x86, msr, cpumask: Use struct cpumask rather than the deprecated cpumask_t

This makes the declarations match the definitions, which already
use 'struct cpumask'.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Borislav Petkov <borislav.petkov@amd.com>
LKML-Reference: <200911052245.41803.rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>