tcg: Move TCGv, dup_const_tl definitions to tcg-op.h

These two items are the last uses of TARGET_LONG_BITS within tcg.h,
and are more in common with the other "_tl" definitions within that file.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>