Tighten up TCGv_i32 vs TCGv type usage. Avoid using TCGv when
TCGv_i32 should be used.

This is in preparation for adding 64bit addressing support.
No functional change.
Reviewed-by: NAlistair Francis <alistair.francis@wdc.com>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: NEdgar E. Iglesias <edgar.iglesias@xilinx.com>