amd/kvm: do not intercept new MSRs for spectre v2 mitigation

amd/kvm: do not intercept new MSRs for spectre v2 mitigation

Do not intercept MSR_IA32_SPEC_CTRL and MSR_IA32_PRED_CMD on AMD
for Spectre v2 mitigation.
As IBRS is not used on AMD, attempt to intercept MSR_IA32_SPEC_CTRL
will have guest crash with injected GP fault.
Also change the comment about field 'always' in svm_direct_access_msrs structure
for clarity.

OraBug: 27370258

Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Håkon Bugge <haakon.bugge@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>