memblock tests: add command line help option

Add a help command line option to the help message. Add the help option
to the short and long options so it will be recognized as a valid
option.

Usage:
    $ ./main -h

    Or:
    $ ./main --help

Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Rebecca Mckeever <remckee0@gmail.com>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Link: https://lore.kernel.org/r/0f3b93a79de78c0da1ca90f74fe35e9a85c7cf93.1660451025.git.remckee0@gmail.com