OMAP2+: hwmod: allow multiple calls to omap_hwmod_init()

There's no longer any reason why we should prevent multiple
calls to omap_hwmod_init().  It is now simply used to register an
array of hwmods.

This should allow a subset of hwmods (e.g., hwmods
handling the system clocksource and clockevents) to be registered
earlier than the remaining mass of hwmods.

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