x86: check feature flags after resume

x86: check feature flags after resume

Make sure no previously present features are missing after resume (and
the re-loading of microcode), to avoid later crashes or (likely silent)
hangs / live locks. This doesn't go beyond checking x86_capability[],
but this should be good enough for the immediate need of making sure
that the BIT mitigation MSRs are still available.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Juergen Gross <jgross@suse.com>