[nrf fromtree] bootutil: Add missing MBEDTLS_ASN1_PARSE_C

Need to define MBEDTLS_ASN1_PARSE_C to be able to see ASN1
functions declarations from mbedTLS.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>
(cherry picked from commit c6f5db2)

Author: de-nordic

boot/bootutil/src/image_ed25519.c

@@ -17,6 +17,8 @@
 #ifdef MCUBOOT_SIGN_ED25519
 #include "bootutil/sign_key.h"
 
+/* We are not really using the MBEDTLS but need the ASN.1 parsing functions */
+#define MBEDTLS_ASN1_PARSE_C
 #include "mbedtls/oid.h"
 #include "mbedtls/asn1.h"