accel/tcg: Hide in_same_page outside of a target-specific context

accel/tcg: Hide in_same_page outside of a target-specific context

While there are other methods that could be used to replace
TARGET_PAGE_MASK, the function is not really required outside
the context of target-specific translation.

This makes the header usable by target independent code.

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