Bring in the last round of updates before adding the interrupt support.

Fix the following issues:

- Removed revision from device softc, it isn't used anywhere else out of
  device attach routine;

- Move the duplicated code for verification of valid banks (and pins) to
  a single function;

- Use some macros to simplify the handling of some constants;

- Update some stale comments.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@276173 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f