Replaced MBEDTLS_SHA512_NO_SHA384 with MBEDTLS_SHA384_C

This does not affect users who use the default config.h. MBEDTLS_SHA512_NO_SHA384 was disabled by default, now MBEDTLS_SHA384_C is enabled by default.

If you were using a config file with both MBEDTLS_SHA512_C and MBEDTLS_SHA512_NO_SHA384, then just remove the MBEDTLS_SHA512_NO_SHA384. If you were using a config file with MBEDTLS_SHA512_C and without MBEDTLS_SHA512_NO_SHA384 and you need the SHA-384 algorithm, then add #define MBEDTLS_SHA384_C to your config file.