ECDH: Fix inclusion of platform.h for proper use of MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED
ECDH: Fix inclusion of platform.h for proper use of MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED

ARMmbed/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls