memblock tests: Makefile: add arguments to control verbosity

Add VERBOSE and MEMBLOCK_DEBUG user-provided arguments. VERBOSE will
enable verbose output from Memblock simulator. MEMBLOCK_DEBUG will enable
memblock_dbg() messages.

Update the help message to include VERBOSE and MEMBLOCK_DEBUG. Update
the README to include VERBOSE. The README does not include all available
options and refers to the help message for the remaining options.
Therefore, omit MEMBLOCK_DEBUG from README.

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/5503f3efe82ecef5c99961a1d53003c8ad06cf27.1656907314.git.remckee0@gmail.com