KVM: PPC: E500: Make clear_tlb_refs and clear_tlb1_bitmap static

Host shadow TLB flushing is logic that the guest TLB code should have
no insight about. Declare the internal clear_tlb_refs and clear_tlb1_bitmap
functions static to the host TLB handling file.

Instead of these, we can use the already exported kvmppc_core_flush_tlb().
This gives us a common API across the board to say "please flush any
pending host shadow translation".

Signed-off-by: Alexander Graf <agraf@suse.de>