util/disk_cache: use a helper to compute cache keys

This will allow to hash additional data into the cache keys or even
change the hashing algorithm easily, should we decide to do so.

v2: don't try to compute key (and crash) if cache is disabled

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/util/disk_cache.c

@@ -1063,4 +1063,11 @@ disk_cache_has_key(struct disk_cache *cache, const cache_key key)
    return memcmp(entry, key, CACHE_KEY_SIZE) == 0;
 }
 
+void
+disk_cache_compute_key(struct disk_cache *cache, const void *data, size_t size,
+                       cache_key key)
+{
+   _mesa_sha1_compute(data, size, key);
+}
+
 #endif /* ENABLE_SHADER_CACHE */