Add missing include with Partition class definition

* Fixes a compilation error while compiling the u-boot loader for
  the ARM platform.

Signed-off-by: Augustin Cavalier <waddlesplash@gmail.com>

src/system/boot/platform/u-boot/devices.cpp

@@ -9,6 +9,7 @@
 #include <boot/disk_identifier.h>
 #include <boot/vfs.h>
 #include <boot/platform.h>
+#include <boot/partitions.h>
 #include <boot/stage2.h>
 #include <boot/stdio.h>