The softmmu tlb uses TCG_REG_TMP[0-3], not any of the normally available
registers. Now that we handle overlap betwen inputs and helper arguments,
and have eliminated use of A0, we can allow any allocatable reg.
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>