iwlwifi: mvm: use build-time assertion for fw trigger ID

The firmware debug trigger ID is always a compile-time constant,
so we can use a build-time assertion to validate that it is in
fact a valid constant.

To make that really guaranteed to work, convert this and the
inline function iwl_fw_dbg_trigger_simple_stop() to macros.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>