Clarify the modprobe support

/etc/modprobe.d is only used for options to modprobe
/etc/modules-load.d is only for adding new modules to load
Clarify this distinction in the support files and change setup.py
to put the relevant files in the correct locations.

Change-Id: Ia1bd82bc458145a7141910bb1f09c5e4d87d6057