tcg: Always enable TCGv type checking

tcg: Always enable TCGv type checking

Instead of using structures, which imply some amount of overhead
on certain ABIs, use pointer types.

This actually reduces the size of the binaries vs a NON-debug
build on ppc64 and x86_64, due to a reduction in the number of
sign-extension insns.

Signed-off-by: Richard Henderson <rth@twiddle.net>