fwk: Initialize notifications statically

This commit reworks the notification initialization code to do three
things:

- Introduce a new, configurable, firmware option to configure the
  maximum number of active notifications
- Use this new static define to initialize the framework notifications
  component
- Initialize the notifications component in a constructor function and
  remove the dependency from the module component

Change-Id: Iec3eecc4e078a634544e95f7081afdc9b47d0cbc
Signed-off-by: Chris Kay <chris.kay@arm.com>