iwlwifi: mvm: fix firmware debug restart recording

When we want to stop the recording of the firmware debug
and restart it later without reloading the firmware we
don't need to resend the configuration that comes with
host commands.
Sending those commands confused the hardware and led to
an NMI 0x66.

Change the flow as following:
* read the relevant registers (DBGC_IN_SAMPLE, DBGC_OUT_CTRL)
* clear those registers
* wait for the hardware to complete its write to the buffer
* get the data
* restore the value of those registers (to restart the
  recording)

For early start (where the configuration is already
compiled in the firmware), we don't need to set those
registers after the firmware has been loaded, but only
when we want to restart the recording without having
restarted the firmware.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>