iwlwifi: mvm: add a debug_enable op

D3 debug data is disabled by default. Currently it is done by tampering
the dump mask. Add an operation that will allow this to be changed
without recompilation.

Signed-off-by: Shahar S Matityahu <shahar.s.matityahu@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>