KVM: PPC: bookehv: remove negation for CONFIG_64BIT

Instead if doing

  #ifndef CONFIG_64BIT
  ...
  #else
  ...
  #endif

we should rather do

  #ifdef CONFIG_64BIT
  ...
  #else
  ...
  #endif

which is a lot easier to read. Change the bookehv implementation to
stick with this rule.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>