First, you should not need to clear the cache other than on software upgrades.
Second, are you using latest OH ? All supported bindings I know of should have their dependencies set right, i.e. would take care of loading the serial module/driver.
No there is no file I know of where to simply put that command in, other than to create some script to auto-execute that on UNIX level.
I have the same issue with the unmerged Sony binding. It constantly needs a feature reinstalled by karaf console after I reboot. low on the to do list. My guess is it should have an extra line in the bindings feature.xml file before it is built to install the feature.