nvdimm: Use the namespace guid, not just the device guid

nvdimm: Use the namespace guid, not just the device guid

This makes long-form device paths for nvdimm be:

NVDIMM(pmem-namespace-guid)/NVDIMM(pmem-label-guid)/HD(...)/File(...)

It also conditionally removes our UUID swizzling, because nobody can
figure out what the correct encoding is, and only byteswaps if
LIBEFIBOOT_SWIZZLE_PMEM_UUID is set (to any value) in the environment.

Signed-off-by: Peter Jones <pjones@redhat.com>