x86/emulator: workaround for AMD erratum 573

x86/emulator: workaround for AMD erratum 573

The only cases where we might end up emulating fsincos (as any other
x87 operations without memory operands) are
- when a HVM guest is in real mode (not applicable on AMD)
- between two half page table updates in PAE mode (unlikely, and not
  doing the emulation here does affect only performance, not
  correctness)
- when a guest maliciously (or erroneously) modifies an (MMIO or page
  table update) instruction under emulation (unspecified behavior)

Hence, in order to avoid the erratum to cause harm to the entire host,
don't emulate fsincos on the affected AMD CPU families.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>