x86/AMD: correct certain Fam17 checks

x86/AMD: correct certain Fam17 checks

Commit 3157bb4e13 ("Add MSR support for various feature AMD processor
families") converted certain checks for Fam11 to include families all
the way up to Fam17. The commit having no description, it is hard to
tell whether this was a mechanical dec->hex conversion mistake, or
indeed intended. In any event the NB_CFG handling needs to be restricted
to Fam16 and below: Fam17 doesn't really have such an MSR anymore. As
per observation it's read-zero / write-discard now, so make PV uniformly
(with the exception of pinned Dom0 vCPU-s) behave so, just like HVM
already does.

Mirror the NB_CFG behavior to MSR_FAM10H_MMIO_CONF_BASE as well, except
that here the vendor/model check is kept in place (for now at least).

A non-MMCFG extended config space access mechanism still appears to
exist, but code to deal with it will need to be written down the road,
when it can actually be tested.

Reported-by: Pu Wen <puwen@hygon.cn>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>