dibs: Register ism as dibs device

dibs: Register ism as dibs device

Register ism devices with the dibs layer. Follow-on patches will move
functionality to the dibs layer.

As DIBS is only a shim layer without any dependencies, we can depend ISM
on DIBS without adding indirect dependencies. A follow-on patch will
remove implication of SMC by ISM.

Define struct dibs_dev. Follow-on patches will move more content into
dibs_dev.  The goal of follow-on patches is that ism_dev will only
contain fields that are special for this device driver. The same concept
will apply to other dibs device drivers.

Define dibs_dev_alloc(), dibs_dev_add() and dibs_dev_del() to be called
by dibs device drivers and call them from ism_drv.c
Use ism_dev.dibs for a pointer to dibs_dev.

Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Link: https://patch.msgid.link/20250918110500.1731261-6-wintera@linux.ibm.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>