x86, kvm: correctly access the KVM_CPUID_FEATURES leaf at 0x40000101

When Hyper-V hypervisor leaves are present, KVM must relocate
its own leaves at 0x40000100, because Windows does not look for
Hyper-V leaves at indices other than 0x40000000.  In this case,
the KVM features are at 0x40000101, but the old code would always
look at 0x40000001.

Fix by using kvm_cpuid_base().  This also requires making the
function non-inline, since kvm_cpuid_base() is static.

Fixes: 1085ba7f
Cc: stable@vger.kernel.org
Cc: mtosatti@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>