tcg: Fix indirect lowering vs TCG_OPF_COND_BRANCH

With TCG_OPF_COND_BRANCH, we extended the lifetimes of
globals across extended basic blocks.  This means that
the liveness computed in pass 1 does not kill globals
in the same way as normal temps.

Introduce TYPE_EBB to match this lifetime, so that we
get correct register allocation for the temps that we
introduce during the indirect lowering pass.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Fixes: b4cb76e6 ("tcg: Do not kill globals at conditional branches")
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>