binman: Use the cbfs memlen field only for uncompressed length

binman: Use the cbfs memlen field only for uncompressed length

The purpose of this badly named field is a bit ambiguous. Adjust the code
to use it only to store the uncompressed length of a file, leaving it set
to None if there is no compression used. This makes it easy to see if the
value in this field is relevant / useful.

Also set data_len for compressed fields, since it should be the length of
the compressed data, not the uncompressed data.

Signed-off-by: Simon Glass <sjg@chromium.org>