Have MBEDTLS_TIMING_C require MBEDTLS_HAVE_TIME

Nowadays, the timing module just builds on a function that provides a timer
with millisecond resolution. In terms of platform requirements, this is
almost exactly equivalent to `mbedtls_ms_time()`
provides (`mbedtls_ms_time()` is arguably a little stronger because it is
supposed to last longer than a single timer object, but an application could
start a timer when it starts, so there's no real difference.) So it's a bit
silly that `timing.c` essentially reimplements this. Rely on
`mbedtls_ms_time()` instead.

This is an API break because in Mbed TLS 4.0, it was possible to enable
`MBEDTLS_TIMING_C` without `MBEDTLS_HAVE_TIME`. However, `timing.c` only
provided an implementation for Windows and Unix-like platforms, and on those
platforms, it is very likely that the default implementation of
`MBEDTLS_HAVE_TIME` would also work. (The main exception would be a platform
that has the traditional Unix function `gettimeofday()`, but not the 1990s
novelty `clock_gettime()`.) So make this an official requirement, as a
belated change that really should have gone into 4.0 if we'd taken the time
to dig into it.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

configs/config-ccm-psk-dtls1_2.h

@@ -29,7 +29,7 @@
 #define MBEDTLS_SSL_COOKIE_C
 #define MBEDTLS_SSL_SRV_C
 #define MBEDTLS_SSL_TLS_C
-#define MBEDTLS_TIMING_C
+#define MBEDTLS_TIMING_C //Only used by test programs
 
 /* TLS protocol feature support */
 #define MBEDTLS_KEY_EXCHANGE_PSK_ENABLED

configs/config-symmetric-only.h

@@ -12,5 +12,5 @@
 #define MBEDTLS_ERROR_STRERROR_DUMMY
 #define MBEDTLS_VERSION_FEATURES
 
-#define MBEDTLS_TIMING_C
+#define MBEDTLS_TIMING_C //Only for benchmarking
 #define MBEDTLS_VERSION_C

configs/crypto-config-ccm-psk-tls1_2.h

@@ -26,7 +26,8 @@
 #define MBEDTLS_PSA_CRYPTO_C
 
 /* System support */
-//#define MBEDTLS_HAVE_TIME /* Optionally used in Hello messages */
+/* Optionally used in Hello messages. Needed for DTLS testing. */
+#define MBEDTLS_HAVE_TIME
 /* Other MBEDTLS_HAVE_XXX flags irrelevant for this configuration */
 
 #define MBEDTLS_CTR_DRBG_C

configs/crypto-config-thread.h

@@ -48,6 +48,7 @@
 
 /* System support */
 #define MBEDTLS_HAVE_ASM
+#define MBEDTLS_HAVE_TIME //Only used by test programs
 
 #define MBEDTLS_AES_ROM_TABLES
 #define MBEDTLS_ECP_NIST_OPTIM