OMAP: hwmod: improve documentation, clean up function names

This patch:

- adds more documentation to the hwmod code

- fixes some documentation typos elsewhere in the file

- changes the _sysc_*() function names to appear in (verb, noun) order,
  to match the rest of the function names.

This patch should not result in any functional change.

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