ARM: OMAP2+: hwmod: add support for link registration

Add support for direct IP block interconnect ("link") registration to
the hwmod code via a new function, omap_hwmod_register_links().  This
will replace direct registration of hwmods, and a subsequent patch
will remove omap_hwmod_register().

This change will allow a subsequent patch to remove the hwmod data
link arrays.  This will reduce the size of the hwmod static data and
also make it easier to generate the data files.  It will also make it
possible to share some of the struct omap_hwmod records across
multiple SoCs, since the link array pointers will be removed from the
struct omap_hwmod.

The downside is that boot time will increase.  Minimizing boot time
was the reason why the link arrays were originally introduced.
Removing them will require extra computation during boot to allocate
memory and associate IP blocks with their interconnects.  However,
since the current kernel development focus is on reducing the number
of lines in arch/arm/mach-omap2/, boot time impact is now seemingly
considered a lower priority.

This patch contains additional complexity to reduce the number of
memory allocations required for this change.  This reduces the boot
time impact: total hwmod link registration time was ~ 2655
microseconds with a simple allocation strategy, but is now ~ 549
microseconds[1] with the approach taken by this patch.

1. Measured on a BeagleBoard 35xx @ 500MHz MPU/333 MHz CORE, average
   of 7 samples.  Total uncertainty is +/- 61 microseconds.

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