MLBEDSW-8497: [MLCE] Avoid modifying FC with dynamic weights

 - If a npu op is followed by a convolution op with dynamic
weights the optimized file ends up containing a duplicated
tensor called _cpu.
 - Another problem is also that an empty bias tensor is added
in the reader.
 - The fix is to ignore these cpu ops both in the reader
and the writer.

Change-Id: I476b4f6062e26cca4ba589df694a99ef79b0f6d4
Signed-off-by: Johan Alfven <johan.alfven@arm.com>