tcg/tci: Hoist op_size checking into tci_args_*

tcg/tci: Hoist op_size checking into tci_args_*

This performs the size check while reading the arguments,
which means that we don't have to arrange for it to be
done after the operation.  Which tidies all of the branches.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>