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.h b/3rdparty/p256-m/p256-m_driver_entrypoints.h
index a509ba9..d92a8f0 100644
--- a/3rdparty/p256-m/p256-m_driver_entrypoints.h
+++ b/3rdparty/p256-m/p256-m_driver_entrypoints.h
@@ -21,11 +21,11 @@
 #ifndef P256M_DRIVER_ENTRYPOINTS_H
 #define P256M_DRIVER_ENTRYPOINTS_H
 
-#if defined(MBEDTLS_P256M_EXAMPLE_DRIVER_ENABLED)
+#if defined(MBEDTLS_PSA_P256M_DRIVER_ENABLED)
 #ifndef PSA_CRYPTO_ACCELERATOR_DRIVER_PRESENT
 #define PSA_CRYPTO_ACCELERATOR_DRIVER_PRESENT
 #endif /* PSA_CRYPTO_ACCELERATOR_DRIVER_PRESENT */
-#endif /* MBEDTLS_P256M_EXAMPLE_DRIVER_ENABLED */
+#endif /* MBEDTLS_PSA_P256M_DRIVER_ENABLED */
 
 #include "psa/crypto_types.h"