powerpc/fsl-booke: declare tlbcam_index for use in c

So, KVM needs to read tlbcam_index to know exactly
which TLB1 entry is unused by host.

Signed-off-by: Liu Yu <yu.liu@freescale.com>
Acked-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>