mbedtls: Deactivate platform abstraction

This makes mbedtls use the POSIX API directly and not use the own
abstraction layer.
The size of the ipkg decreased by about 100 bytes.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

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

@@ -210,6 +210,15 @@
  
  /**
   * \def MBEDTLS_MD_C
+@@ -2354,7 +2354,7 @@
+  *
+  * This module enables abstraction of common (libc) functions.
+  */
+-#define MBEDTLS_PLATFORM_C
++//#define MBEDTLS_PLATFORM_C
+ 
+ /**
+  * \def MBEDTLS_RIPEMD160_C
 @@ -2365,7 +2365,7 @@
   * Caller:  library/md.c
   *