iwlwifi: get rid of fw/nvm.c

There's already an opmode common file for nvm iwl-nvm-parse.c
Move the content of fw/nvm.c to iwl-nvm-parse.c and delete fw/nvm.c.

Signed-off-by: Shaul Triebitz <shaul.triebitz@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>