tools/testing/nvdimm: replace CONFIG_DMA_CMA dependency with vmalloc()

DMA_CMA is incompatible with SWIOTLB used in enterprise distro
configurations.  Switch to vmalloc() allocations for all resources.

Acked-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>