Get a good start on cleaning up powermgmt.c
1) Consolidate charging types' code as much as possible at the moment.
2) Remove the iRiver code for the moment. It so happens that it isn't being
compiled anyway so it's just noise. Grab it out of the revision history
when needed again.
3) A small fix to CHARGING_CONTROL where changing of #defines somewhere in
earlier revisions actually ended up having it use the wrong battery filter
constant. A few state variables that were locals but stay in scope for
the life of the power thread get static storage to help separate algorithms.
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@17580 a1c6a512-1295-4272-9138-f99709370657