microblaze: Support system with WB cache

WB cache use different instruction that WT cache but the major code
is that same. That means that wdc.flush on system with WT cache
do the same thing as before.

You need newer toolchain with wdc.flush support.
Signed-off-by: NMichal Simek <monstr@monstr.eu>

arch/microblaze/lib/cache.c

@@ -34,7 +34,7 @@ void flush_cache (ulong addr, ulong size)
 #endif
 				"nop;"
 #ifdef CONFIG_DCACHE
-				"wdc	%0, r0;"
+				"wdc.flush	%0, r0;"
 #endif
 				"nop;"
 				: