[CORE] vmm_devtree: Improve nodeid table implementation

The current nodeid table implementation did not provide any mechanism
to distinguish nodeid table enteries.

In future, we might have multiple subsystems and frameworks using
nodeid table APIs. These subsystems and frameworks will be mostly
interested in nodeid table enteries belonging to themselves.

This patch adds support for distinguishing nodeid table enteries by
introducing subsystem name member in struct vmm_devtree_nidtbl_entry
and improving existing nodeid table APIs accordingly.

Signed-off-by: Anup Patel <anup@brainfault.org>