ARM: OMAP2+: hwmod: reorganize and document the initialization process

Reorganize the code involved in initializing the internal data for
each hwmod to make it easier to read and maintain.  This involves
improving documentation and removing some duplicated and unnecessary
code.

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