MBEDTLS_AES_ROM_TABLES macro

\def MBEDTLS_AES_ROM_TABLES Use precomputed AES tables stored in ROM. Uncomment this macro to use precomputed AES tables stored in ROM. Comment this macro to generate AES tables in RAM at runtime. Tradeoff: Using precomputed ROM tables reduces RAM usage by ~8kb (or ~2kb if \c MBEDTLS_AES_FEWER_TABLES is used) and reduces the initialization time before the first AES operation can be performed. It comes at the cost of additional ~8kb ROM use (resp. ~2kb if \c MBEDTLS_AES_FEWER_TABLES below is used), and potentially degraded performance if ROM access is slower than RAM access. This option is independent of \c MBEDTLS_AES_FEWER_TABLES.