OMAP2/3/4 core: create omap_device layer

OMAP2/3/4 core: create omap_device layer

The omap_device code provides a mapping of omap_hwmod structures into
the platform_device system, and includes some details on external
(board-level) integration.  This allows drivers to enable, idle, and
shutdown on-chip device resources, including clocks, regulators, etc.
The resources enabled and idled are dependent on the device's maximum
wakeup latency constraint (if present).

At the moment, omap_device functions are intended to be called from
platform_data function pointers.  Ideally in the future these
functions will be called from either subarchitecture-specific
platform_data activate, deactivate functions, or via an custom
bus/device type for OMAP.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Benoit Cousson <b-cousson@ti.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Rajendra Nayak <rnayak@ti.com>
Cc: Vikram Pandita <vikram.pandita@ti.com>
Cc: Sakari Poussa <sakari.poussa@nokia.com>
Cc: Anand Sawant <sawant@ti.com>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: Eric Thomas <ethomas@ti.com>
Cc: Richard Woodruff <r-woodruff2@ti.com>