TCG: Fix tcg_gen_extr_i64_tl for 32bit

We expose a generic helper "tcg_gen_extr_i64_tl" for 64bit targets, but the
same function for 32bit targets is a misnomer and refers to an invalid function
name.

Fix up the definition to point to the correct internal helper names instead.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Richard Henderson <rth@twiddle.net>