test: Use ut_asserteq_mem() where possible

Quite a few tests still use ut_assertok(memcmp(...)) and variants. Modify
them to use the macro designed for this purpose.

Suggested-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>