iwlwifi: mvm: add debugfs entry to trigger a dump as any time-point

This is used for different tests collecting different types of
debug data from fw (e.g latency issues, hw issues etc).

Signed-off-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210131201908.0db829694810.I001f39d34ae46c87870d9bd94a4baaa3250578d1@changeid
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>