The old code was using smp_call_function_many which skips the current
cpu if it is in the supplied cpumask. Switch to the rdmsr_on_cpus()
interface which takes care of that.

In addition, add get_cpus_on_this_dct_cpumask helper which computes a
cpumask of all the cores on a node and thus on a DCT.
Signed-off-by: NBorislav Petkov <borislav.petkov@amd.com>