build: W600-SDK importiert, Firmware-Build und Hello am EVK

Docker-Build mit gcc-arm-none-eabi 4.9-2014q4 (statt Homebrew-Cask) verwendet,
Dockerfile/tools/docker.sh dafür aus Task 13 vorgezogen. cmake/sdk.cmake schont
gcc 4.9 (kennt -fcommon/-Wno-error=... nicht). Zwei zusätzliche SDK-Stubs
(EarlyInit, pre_gpio_config) in src/sys/sdk_stubs.c ergänzt, siehe sdk/PATCHES.md.

src/sys/nl_fwup_hook.h

@@ -0,0 +1,12 @@
+#ifndef NL_FWUP_HOOK_H
+#define NL_FWUP_HOOK_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+/* Called by the SDK updater (sdk/Platform/Common/fwup/wm_fwup.c) after the image CRC
+ * matched. sha256 covers the T_BOOTER header plus payload, tail is the 512 byte block
+ * appended to the image. Return true to accept the image. */
+bool nl_fwup_verify_tail(const uint8_t sha256[32], const uint8_t *tail, uint32_t tail_len);
+
+#endif