KVM: SVM: Initialize fpu_active in init_vmcb()

init_vmcb() sets up the intercepts as if the fpu is active, so initialize it
there.  This avoids an INIT from setting up intercepts inconsistent with
fpu_active.

Acked-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>