Shanling Q1: Support OF-initiated firmware updates

It's now possible to install OF updates on a rockboxed Shanling Q1.
Previously these didn't work because the RB bootloader interrupted
the update process.

Updates will proceed as they normally do on a non-Rockboxed Q1,
except at the end of the update you'll reboot to Rockbox instead
of the OF. This is only a minor inconvienience and doesn't affect
the update process.

Change-Id: I0f8fc96f073c50c1512bf60e0927491be8178eb0

bootloader/x1000/main.c

@@ -43,8 +43,10 @@ static int read_btn(void)
 #endif
 }
 
-void main(void)
+void main(uint32_t saved_cpm_scratch)
 {
+    (void)saved_cpm_scratch;
+
     system_init();
     core_allocator_init();
     kernel_init();
@@ -71,6 +73,16 @@ void main(void)
      * present, blocking with an "insert SD card" prompt if appropriate. */
     disk_mount_all();
 
+#ifdef SHANLING_Q1
+    /* This is needed for OF updates. The OF extracts the update package
+     * to the SD card and reboots to the recovery kernel to complete the
+     * update. */
+    if ((saved_cpm_scratch & 0xffff) == 0x1a1a) {
+        cpm_scratch_set(saved_cpm_scratch & 0xffff0000);
+        boot_of_recovery();
+    }
+#endif
+
     /* If USB booting, the user probably needs to enter recovery mode;
      * let's not force them to hold down the recovery key. */
     bool recovery_mode = get_boot_flag(BOOT_FLAG_USB_BOOT);