Give a production-sounding name to the p256m option

Now that p256-m is officially a production feature and not just an example,
give it a more suitable name.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/3rdparty/p256-m/p256-m_driver_entrypoints.c b/3rdparty/p256-m/p256-m_driver_entrypoints.c
index b2236e4..7709301 100644
--- a/3rdparty/p256-m/p256-m_driver_entrypoints.c
+++ b/3rdparty/p256-m/p256-m_driver_entrypoints.c
@@ -26,7 +26,7 @@
 #include <stddef.h>
 #include <string.h>
 
-#if defined(MBEDTLS_P256M_EXAMPLE_DRIVER_ENABLED)
+#if defined(MBEDTLS_PSA_P256M_DRIVER_ENABLED)
 
 /* INFORMATION ON PSA KEY EXPORT FORMATS:
  *
@@ -321,4 +321,4 @@
     return status;
 }
 
-#endif /* MBEDTLS_P256M_EXAMPLE_DRIVER_ENABLED */
+#endif /* MBEDTLS_PSA_P256M_DRIVER_ENABLED */