Expose omap_device_{alloc, delete, register} so we can use them outside
of omap_device.c.

This approach allows users, which need to manipulate an archdata member
of a device before it is registered, to do so. This is also useful
for users who have their devices created very early so they can be used
at ->reserve() time to reserve CMA memory.

The immediate use case for this is to set the private iommu archdata
member, which binds a device to its associated iommu controller.
This way, generic code will be able to attach omap devices to their
iommus, without calling any omap-specific API.

With this in hand, we can further clean the existing mainline OMAP iommu
driver and its mainline users, and focus on generic IOMMU approaches
for future users (rpmsg/remoteproc and the upcoming generic DMA API).

This patch is still considered an interim solution until DT fully materializes
for omap; at that point, this functionality will be removed as DT will
take care of creating the devices and configuring them correctly.

Tested on OMAP4 with a generic rpmsg/remoteproc that doesn't use any
omap-specific IOMMU API anymore.
Signed-off-by: NOhad Ben-Cohen <ohad@wizery.com>
Signed-off-by: NKevin Hilman <khilman@ti.com>
Signed-off-by: NTony Lindgren <tony@atomide.com>