tcg/cputlb: remove other-cpu capability from TLB flushing

tcg/cputlb: remove other-cpu capability from TLB flushing

Some TLB flush operations can flush other CPUs. The problem with this
is they used non-synced variants of flushes (i.e., that return
before the destination has completed the flush). Since all TLB flush
users need the _synced variants, and that last user (ppc) of the
non-synced flush was buggy, this is a footgun waiting to go off. There
do not seem to be any callers that flush other CPUs, so remove the
capability.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>