tests: ztest: Add zassert_mem_equal()
tests: ztest: Add zassert_mem_equal()

Allows to compare 2 memory areas for equality.

Signed-off-by: Paul Sokolovsky <35cb557f011771c94f127d6fef99f804b62203f5@linaro.org>

zephyrproject-rtos/zephyr,explora26/zephyr,nashif/zephyr,Vudentz/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,nashif/zephyr,Vudentz/zephyr,Vudentz/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,explora26/zephyr,Vudentz/zephyr,explora26/zephyr,Vudentz/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,galak/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,ldts/zephyr,explora26/zephyr,Vudentz/zephyr,finikorg/zephyr,finikorg/zephyr,ldts/zephyr