tests: settings: move to new ztest API

test cases in tests/subsys/settings/fcb, tests/subsys/settings/littlefs,
tests/subsys/setttings/nvs all depend on tests/subsys/settings/src and
tests/subsys/settings/fs, so update them in one commit.

Signed-off-by: Meng xianglin <xianglinx.meng@intel.com>