firmware: arm_ffa: Add checks for the notification enabled state

We need to check if the FF-A notifications are enabled or not in all
the notification operations that are accessible for the FF-A device
from the FF-A driver. This helps to avoid making calls to the FF-A
firmware even if the notification setup has failed.

Link: https://lore.kernel.org/r/20231024-ffa-notification-fixes-v1-3-d552c0ec260d@arm.com


Tested-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>