KVM: x86: Use double-underscore read/write MSR helpers as appropriate

KVM: x86: Use double-underscore read/write MSR helpers as appropriate

Use the double-underscore helpers for emulating MSR reads and writes in
he no-underscore versions to better capture the relationship between the
two sets of APIs (the double-underscore versions don't honor userspace MSR
filters).

No functional change intended.

Signed-off-by: Chao Gao <chao.gao@intel.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Link: https://lore.kernel.org/r/20250812025606.74625-3-chao.gao@intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>