platform: nordic_nrf: Fix assert in initialization

This fixes an erroneous attempt to configure the FPU
peripheral in NRF91 series. The FPU is not configurable
in NRF91 series and it is always non-secure. This caused
a failed assertion in the initialzation since the FPU
present field is not set for the SPU configuration.

This change configures the FPU only in NRF53 series devices
which have a configurable FPU.

Signed-off-by: Georgios Vasilakis <georgios.vasilakis@nordicsemi.no>
Change-Id: Ia00e0e620ab51850e6ee8b382e5d03a245b6db0c
diff --git a/platform/ext/target/nordic_nrf/common/core/target_cfg.c b/platform/ext/target/nordic_nrf/common/core/target_cfg.c
index 502b644..479eafe 100644
--- a/platform/ext/target/nordic_nrf/common/core/target_cfg.c
+++ b/platform/ext/target/nordic_nrf/common/core/target_cfg.c
@@ -767,10 +767,13 @@
     /* Peripheral configuration */
 
     /* The following peripherals share ID:
-     * - FPU
+     * - FPU (FPU cannot be configured in NRF91 series, it's always NS)
      * - DCNF (On 53, but not 91)
      */
+#ifndef NRF91_SERIES
     spu_peripheral_config_non_secure((uint32_t)NRF_FPU, false);
+#endif
+
     /* The following peripherals share ID:
      * - REGULATORS
      * - OSCILLATORS