product/juno: Improve transport module init sequence

At present, the transport module delays the initialization of
the shared memory channel due to dependency on the power domain
responsible for the shared memory. The transport module registers
a notification for the status of this power domain and waits
for powered on notification, it will then initialize the channel
once it receives power on notification from the power domain module.
However, for some platforms power domain can be initialized early
using default_power_on = true setting in respective
platform-specific config_ppu*.c as many platforms have its shared
memory in the SYSTOP power domain which is usually enabled by default.
The reason we need above early initialization because few other
modules would not be proceeding without the transport module channel
initialization which would further interact with the transport module
using notifications, thus deferring its initialization.
If we can initialize the transport module early we can also
initialize other modules early too.

This change removes scmi module notificiation that depend on
transport module

Change-Id: I88cf796a368d2ec31efa4a3498f95a9d0a8fe4db
Signed-off-by: Girish Pathak <girish.pathak@arm.com>