Stop specializing on TARGET_LONG_BITS == 32; unconditionally allocate
a temp and expand with tcg_gen_extu_i32_tl.  Split out gen_aa32_addr,
gen_aa32_frob64, gen_aa32_ld_i32 and gen_aa32_st_i32 as separate interfaces.
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NRichard Henderson <rth@twiddle.net>