Add an entry for CPUID_7_1_EAX in the reserve_cpuid array in preparation
for incorporating the array in bit() build-time assertions, specifically
to avoid an assertion on F(AVX512_BF16) in do_cpuid_7_mask().

No functional change intended.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>