Combine the two files into cacheflush.c.  There's a couple of bits
that would be helpful to share between the two, and combining them
seems better than exporting the bits.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20220621014837.189139-2-richard.henderson@linaro.org>