iwlwifi: Add more call-sites for pcie reg dumper

Commit a6d24fad ("iwlwifi: pcie: dump registers when HW becomes
inaccessible") added a function to dump pcie config registers and
memory mapped registers on a failure. It is currently only accessible
within trans.c. Add it to struct iwl_trans_ops, so that failure cases
in other files can call it.  While there, add a call to this function
from iwl_pcie_load_firmware_chunk in pcie/tx.c, since this is a common
failure case seen on some platforms.

Signed-off-by: Kirtika Ruchandani <kirtika@chromium.org>
[modified the commit message slightly]
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>