OMAP hwmod: add hwmod class support

Add support for categorizing and iterating over hardware IP blocks by
the "class" of the IP block.  The class is the type of the IP block:
e.g., "timer", "timer1ms", etc.  Move the OCP_SYSCONFIG/SYSSTATUS data
from the struct omap_hwmod into the struct omap_hwmod_class, since
it's expected to stay consistent for each class.  While here, fix some
comments.

The hwmod_class structures in this patch were designed and proposed by
Benoît Cousson <b-cousson@ti.com> and were refined in a discussion
between Thara Gopinath <thara@ti.com>, Kevin Hilman
<khilman@deeprootsystems.com>, and myself.

This patch uses WARN() lines that are longer than 80 characters, as
Kevin noted a broader lkml consensus to increase greppability by
keeping the messages all on one line.

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