Enable cache on ARM U-Boot port.

Without it the port is reidiculously slow.

grub-core/kern/uboot/init.c

@@ -31,6 +31,7 @@
 #include <grub/uboot/uboot.h>
 #include <grub/uboot/api_public.h>
 #include <grub/cpu/system.h>
+#include <grub/cache.h>
 
 extern char __bss_start[];
 extern char _end[];
@@ -107,6 +108,11 @@ grub_machine_init (void)
   /* Enumerate memory and initialize the memory management system. */
   grub_uboot_mm_init ();
 
+  /* Should be earlier but it needs memalign.  */
+#ifdef __arm__
+  grub_arm_enable_caches_mmu ();
+#endif
+
   grub_dprintf ("init", "__bss_start: %p\n", __bss_start);
   grub_dprintf ("init", "_end: %p\n", _end);
   grub_dprintf ("init", "grub_modbase: %p\n", (void *) grub_modbase);