KVM: selftests: Assert that XTILE_DATA is set in IA32_XFD on #NM

KVM: selftests: Assert that XTILE_DATA is set in IA32_XFD on #NM

Add an extra check to IA32_XFD to ensure that XTILE_DATA is actually set,
i.e. is consistent with the AMX architecture. In addition, repeat the
checks after the guest/host world switch to ensure the values of IA32_XFD
and IA32_XFD_ERR are well preserved.

Signed-off-by: Mingwei Zhang <mizhang@google.com>
Link: https://lore.kernel.org/r/20230221163655.920289-7-mizhang@google.com
[sean: massage changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>