current critical section implementation makes possible that interrupt

signals are lost. It was observed at last for tests-api-spi ci-test-shield's
test.

This patch introduce usage of sdk5 origin implementation in which
sd_nvic_critical_region_enter/exit is calling each time critical region
is enter/exit. This fixes the issue.

Author: nvlsianpu

targets/TARGET_NORDIC/TARGET_NRF5/nordic_critical.c

@@ -15,43 +15,17 @@
  * limitations under the License.
  */
 
-#include <stdint.h>                  // uint32_t, UINT32_MAX
-#include <assert.h>                  // uint32_t, UINT32_MAX
-#include "cmsis.h"
-#include "nrf_soc.h"
-#include "nrf_sdm.h"
-#include "nrf_nvic.h"
+#include <stdint.h>
+#include "app_util_platform.h"
 
-static uint8_t  _sd_state = 0;
-static volatile uint32_t _entry_count = 0;
+static uint8_t nordic_cr_nested = 0;
 
 void core_util_critical_section_enter()
 {
-    // if a critical section has already been entered, just update the counter
-    if (_entry_count) {
-        ++_entry_count;
-        return;
-    }
-
-    // in this path, a critical section has never been entered
-    // routine of SD V11 work even if the softdevice is not active
-    sd_nvic_critical_region_enter(&_sd_state);
-
-    assert(_entry_count == 0); // entry count should always be equal to 0 at this point
-    ++_entry_count;
+    app_util_critical_region_enter(&nordic_cr_nested);
 }
 
 void core_util_critical_section_exit()
 {
-    assert(_entry_count > 0);
-    --_entry_count;
-
-    // If their is other segments which have entered the critical section, just leave
-    if (_entry_count) {
-        return;
-    }
-
-    // This is the last segment of the critical section, state should be restored as before entering
-    // the critical section
-    sd_nvic_critical_region_exit(_sd_state);
+    app_util_critical_region_exit(nordic_cr_nested);
 }