tcg/sparc: Use tcg_out_movi_imm13 in tcg_out_addsub2_i64

tcg/sparc: Use tcg_out_movi_imm13 in tcg_out_addsub2_i64

When BH is constant, it is constrained to 11 bits for use in MOVCC.
For the cases in which we must load the constant BH into a register,
we do not need the full logic of tcg_out_movi; we can use the simpler
function for emitting a 13 bit constant.

This eliminates the only case in which TCG_REG_T2 was passed to
tcg_out_movi, which will shortly become invalid.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>