mbedtls: Disable MBEDTLS_SHA256_SMALLER implementation

Disable MBEDTLS_SHA256_SMALLER implementation, not enabled by default in
upstream and reduces performance by quite a bit.

Source: include/mbedtls/config.h

Enable an implementation of SHA-256 that has lower ROM footprint but also
lower performance.

The default implementation is meant to be a reasonnable compromise between
performance and size. This version optimizes more aggressively for size at
the expense of performance. Eg on Cortex-M4 it reduces the size of
mbedtls_sha256_process() from ~2KB to ~0.5KB for a performance hit of
about 30%.

The size of mbedtls increased a little bit:
ipkg for mips_24kc before:
164.382 Bytes
ipkg for mips_24kc after:
166.240 Bytes

Signed-off-by: Daniel Engberg <[email protected]>

package/libs/mbedtls/patches/200-config.patch

@@ -126,15 +126,6 @@
 
  /**
   * \def MBEDTLS_SHA256_SMALLER
-@@ -1134,7 +1134,7 @@
-  *
-  * Uncomment to enable the smaller implementation of SHA256.
-  */
--//#define MBEDTLS_SHA256_SMALLER
-+#define MBEDTLS_SHA256_SMALLER
-
- /**
-  * \def MBEDTLS_SSL_ALL_ALERT_MESSAGES
 @@ -1272,7 +1272,7 @@
   *          configuration of this extension).
   *