esoc: Add support for client hooks based on priority

Some subsystems/drivers require notifications from the esoc
driver as soon as the it powers on/off the modem.
For this, the clients cannot directly depend on the
SSR notifications.

Hence, adding support such that the clients who are
interested in listening to such events can register
themselves. Moreover, the order in which these notifications
are sent to the clients can be prioritized statically.

Also, a flexibilty is added such that the user-space
can get information, such as link-id, from the interested
client.

Change-Id: I8274f0fd5210b7d0186dddf63afd69fc98d2e110
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>