microblaze: Flush caches before enabling them

Flushing caches is necessary because of soft reset
which doesn't clear caches.

Signed-off-by: Michal Simek <monstr@monstr.eu>
Reviewed-by: Marek Vasut <marex@denx.de>
diff --git a/include/configs/microblaze-generic.h b/include/configs/microblaze-generic.h
index 721cd90..eed38c1 100644
--- a/include/configs/microblaze-generic.h
+++ b/include/configs/microblaze-generic.h
@@ -287,6 +287,10 @@
 # undef CONFIG_DCACHE
 #endif
 
+#ifndef XILINX_DCACHE_BYTE_SIZE
+#define XILINX_DCACHE_BYTE_SIZE	32768
+#endif
+
 /*
  * BOOTP options
  */