tests: mem_map: compare just written data too in mapped_rw
tests: mem_map: compare just written data too in mapped_rw

After writing to mapped_rw, we should also check if the backing
buffer has the correct data. Or we could have a situation where
on systems that need explicit cache controls, the newly updated
mapped_rw is cached but the backing buffer still contain old
data. Comparing the backing buffer to mapped_ro does not really
matter in this case as the content would certain match.

Also, this moves the mapping of mapped_ro earlier so that we
map both mapped_rw and mapped_ro because data manipulation.

And that we also need to verify the values of the backing and
mapped buffers.

Signed-off-by: Daniel Leung <d94e04d205b5962d7873a139ef298b03c1717f72@intel.com>

zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr