iwlwifi: dbg: split fifos dump

Split the dump of RXF and TXF. This is in order to
enable code reuse for INI, which may decide to dump
only RXF and not TXF, and vice versa.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>