[nrf noup] mcuboot: Prevent PSA crypto driver requirements

-This commit adds MBEDTLS_PSA_CRYPTO_CLIENT to the config-file
 that MCUboot uses, to ensure that we are not requesting details
 about PSA crypto drivers. When MBEDTLS_PSA_CRYPTO_CLIENT is set
 and not MBEDTLS_PSA_CRYPTO_C, then we are preventing from figuring
 out what the PSA crypto driver contexts structures look like...
 please see a comment in psa/crypto_structs.h for details

Signed-off-by: Frank Audun Kvamtrø <frank.kvamtro@nordicsemi.no>

boot/zephyr/include/mcuboot-mbedtls-cfg.h

@@ -32,5 +32,8 @@
 #else
 #error "Cannot configure mbedTLS; signature type is unknown."
 #endif
-
+/* This define prevents include of psa/crypto from requing knowledge of the 
+ * PSA crypto drivers. see psa/crypto_structs.h for details
+ */
+#define MBEDTLS_PSA_CRYPTO_CLIENT
 #endif