sys_util: mmap: add slice, obj, mem and mapped file tests
sys_util: mmap: add slice, obj, mem and mapped file tests

Signed-off-by: Constantin Musca <e6b0bba089ab6d3e8fde8b62faae63e6b21d7743@amazon.com>

firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker