ngd_slim: Register with QMI service in the slave-notification thread

Slave notification thread is used to notify slaves when QMI server
(hosted by slimbus msater driver) on the remote execution environment
has come up. Use that thread's entry point to do QMI service
registration as well since doing so in probe may trigger another
probe by the QMI service leading to boot-up stalling.

Change-Id: I06b1bcfd9aa3d570554971acacd5d7b1dc20fd1c
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>