OMAP2+: hwmod: fix a warning, add some docs, remove unused fields

Trivial cleanup and documentation changes on the hwmod code and data:

- add some hwmod documentation to indicate flags that should be moved
  outside the static hwmod data in a future patch

- remove some unused fields in the struct omap_hwmod_ocp_if and
  struct omap_hwmod structures

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Benoît Cousson <b-cousson@ti.com>