Add Mbed TLS Platform module errors

1. Add error codes for platform setup \ teardown.
2. Reassign `reference_count` to 0 after terminating platform,
and remove condition for 0

Author: Ron Eldor

features/cryptocell/FEATURE_CRYPTOCELL310/TARGET_MCU_NRF52840/crypto_platform.c

@@ -34,7 +34,7 @@ int crypto_platform_setup( crypto_platform_ctx *ctx )
     NRF_CRYPTOCELL->ENABLE = 1;
 
     if( SaSi_LibInit( &rndState, &rndWorkBuff ) != 0 )
-          return ( -1 );
+          return ( MBEDTLS_PLATFORM_HW_FAILED );
 
     return ( 0 );
 }

features/mbedtls/platform/inc/platform_mbed.h

@@ -24,3 +24,6 @@
 #if defined(MBEDTLS_CONFIG_HW_SUPPORT)
 #include "mbedtls_device.h"
 #endif
+
+#define MBEDTLS_PLATFORM_INVALID_DATA    -0x0080
+#define MBEDTLS_PLATFORM_HW_FAILED       -0x0082

features/mbedtls/platform/src/platform_alt.c

@@ -27,7 +27,7 @@ int mbedtls_platform_setup( mbedtls_platform_context *ctx )
 {
     int ret = 0;
     if( ctx == NULL )
-        return ( -1 );
+        return ( MBEDTLS_PLATFORM_INVALID_DATA );
 
     reference_count++;
 
@@ -44,15 +44,13 @@ void mbedtls_platform_teardown( mbedtls_platform_context *ctx )
     if( ctx == NULL )
         return;
 
-    if( reference_count == 0 )
-        return;
-
     reference_count--;
 
-    if( reference_count == 0 )
+    if( reference_count <= 0 )
     {
         /* call platform specific code to terminate crypto driver*/
         crypto_platform_terminate( &ctx->platform_impl_ctx );
+        reference_count = 0;
     }
 }