pstore/ram: Report backend assignments with finer granularity

In order to more easily perform automated regression testing, this
adds pr_debug() calls to report each prz allocation which can then be
verified against persistent storage. Specifically, seeing the dividing
line between header, data, any ECC bytes. (And the general assignment
output is updated to remove the bogus ECC blocksize which isn't actually
recorded outside the prz instance.)

Signed-off-by: Kees Cook <keescook@chromium.org>