x86: svm: check TSC adjust support

MSR_IA32_TSC_ADJUST may be supported by KVM on AMD machines, but it does
not show on AMD manual. Check CPUID to see if it supported before
running the relevant tests.

Signed-off-by: Nadav Amit <namit@vmware.com>
Message-Id: <20200630094516.22983-3-namit@vmware.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>