Add AES HW encryption for NUCLEO_F756ZG in mbedtls

[adustm]

Description

Enable HW acceleration for AES ECB + CBC on STM32F756ZG
aes_alt.c is compatible between STM32F4 and F7. Only defines have been necessary.

Status

READY

Steps to test or reproduce

To test this feature, you have to modify TESTS/mbedtls/selfttest/main.cpp in order to call aes self test:
add:
#include "mbedtls/aes.h"
then

#if defined(MBEDTLS_AES_C)
MBEDTLS_SELF_TEST_TEST_CASE(mbedtls_aes_self_test)
#endif

then

#if defined(MBEDTLS_AES_C)
    Case("mbedtls_aes_self_test", mbedtls_aes_self_test_test_case),
#endif

[sg-]

@adustm Can this be moved against the workshop branch?