esoc: Add support to allow SSR framework to read esoc dt node

For a subsystem to register with the SSR framework, a
subsys_register call is made by the driver pertaining
to the subsystem. The subsys descriptor parameter that
is passed with this call is expected to have it's device
of_node structure to be filled for the subsystem_restart
driver to access certain information about the subsystem.

Fill the of_node structure for esoc. This change is needed
for the subsystem_restart driver to read the ssctl instance
id property for esoc.

Change-Id: Ic8eef38390ac423210cbddff76fab51b09f331b6
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>