firmware: arm_ffa: Refactoring to prepare for framework notification support

Currently, the framework notifications are not supported at all.
handle_notif_callbacks() doesn't handle them though it is called with
framework bitmap. Make that explicit by adding checks for the same.

Also, we need to further classify the framework notifications as Secure
Partition Manager(SPM) and NonSecure Hypervisor(NS_HYP). Extend/change
notify_type enumeration to accommodate all the 4 type and rejig the
values so that it can be reused in the bitmap enable mask macros.

While at this, move ffa_notify_type_get() so that it can be used in
notifier_hash_node_get() in the future.

No functional change.

Tested-by: Viresh Kumar <viresh.kumar@linaro.org>
Message-Id: <20250217-ffa_updates-v3-14-bd1d9de615e7@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>