memblock test: Modify the obsolete description in README

The VERBOSE option in Makefile has been moved, but there still have the
description left in README. For now, we use `-v` options when running
memblock test to print information, so using the new to replace the
obsolete items.

Signed-off-by: Shaoqin Huang <shaoqin.huang@intel.com>
Acked-by: Rebecca Mckeever <remckee0@gmail.com>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Link: https://lore.kernel.org/r/20220729161125.190845-1-shaoqin.huang@intel.com