kvm: svm: Update svm_xsaves_supported

AMD CPUs now support XSAVES in a limited fashion (they require IA32_XSS
to be zero).

AMD has no equivalent of Intel's "Enable XSAVES/XRSTORS" VM-execution
control. Instead, XSAVES is always available to the guest when supported
on the host.

Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Aaron Lewis <aaronlewis@google.com>
Change-Id: I40dc2c682eb0d38c2208d95d5eb7bbb6c47f6317
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm.c

@@ -5973,7 +5973,7 @@ static bool svm_mpx_supported(void)
 
 static bool svm_xsaves_supported(void)
 {
-	return false;
+	return boot_cpu_has(X86_FEATURE_XSAVES);
 }
 
 static bool svm_umip_emulated(void)