KVM: SVM: Fix x2APIC MSRs interception

The index for svm_direct_access_msrs was incorrectly initialized with
the APIC MMIO register macros. Fix by introducing a macro for calculating
x2APIC MSRs.

Fixes: 5c127c85 ("KVM: SVM: Adding support for configuring x2APIC MSRs interception")
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Message-Id: <20220718083833.222117-1-suravee.suthikulpanit@amd.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>