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
diff --git a/drivers/arm/ethosn/ethosn_smc.c b/drivers/arm/ethosn/ethosn_smc.c
index cf34910..6b1ab85 100644
--- a/drivers/arm/ethosn/ethosn_smc.c
+++ b/drivers/arm/ethosn/ethosn_smc.c
@@ -286,3 +286,13 @@
 		SMC_RET1(handle, SMC_UNK);
 	}
 }
+
+int ethosn_smc_setup(void)
+{
+	if (ETHOSN_NUM_DEVICES == 0U) {
+		ERROR("ETHOSN: No NPU found\n");
+		return ETHOSN_FAILURE;
+	}
+
+	return 0;
+}