feat(ethos-n): add check for NPU in SiP setup

feat(ethos-n): add check for NPU in SiP setup

The SiP service in the Arm(R) Ethos(TM)-N NPU driver requires that there
is at least one NPU available. If there is no NPU available, the driver
is either used incorrectly or the HW config is incorrect.

To ensure that the SiP service is not incorrectly used, a setup handler
has been added to the service that will validate that there is at least
one NPU available.

Signed-off-by: Mikael Olsson <mikael.olsson@arm.com>
Change-Id: I8139a652f265cfc0db4a37464f39f1fb92868e10