[mbed-tls] Adding option to disable the zeroisation of internal buffers

After recently updating mbedtls I noticed a considerable slowdown (over 70% on my cortex-m7 board) in the sha256 implementation, and after some digging I found the offending commit: https://github.com/Mbed-TLS/mbedtls/commit/76749aea784cfec245390d0d6f0ab0a2d...

I understand the motivation behind the commit, but I think it may not be relevant to all use cases. So my question is if an option to disable the clearing of internal buffers in mbedtls_config.h would be a reasonable improvement? Or would that be considered to much of a foot gun? Regards, Joel Petersson