target/arm: Move combine_cacheattrs and subroutines to ptw.c

target/arm: Move combine_cacheattrs and subroutines to ptw.c

There are a handful of helpers for combine_cacheattrs
that we can move at the same time as the main entry point.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220604040607.269301-15-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>