iwlagn: combine firmware code/data

On new hardware, ucode images always come in
pairs: code and data. Therefore, combine the
variables into an appropriate struct and use
that when both code and data are needed.

Also, combine allocation and copying so that
we have less code in total.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>