tcg: Add mmu helpers that take a return address argument

tcg: Add mmu helpers that take a return address argument

Allow the code that tcg generates to be less obtuse, passing in
the return address directly instead of computing it in the helper.

Maintain the old entrance point unchanged as an alternate entry point.

Delete the helper_st*_cmmu prototypes; the implementations did not exist.

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