linux-user: log page table changes under -d page

linux-user: log page table changes under -d page

The CPU_LOG_PAGE flag is woefully underused and could stand to do
extra duty tracking page changes. If the user doesn't want to see the
details as things change they still have the tracepoints available.

We push the locking into log_page_dump and pass a reason for the
banner text.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20191205122518.10010-5-alex.bennee@linaro.org>