Blackfin: check for anomaly 05000475

Parts that have on-chip L2 SRAM cannot safely utilize writeback caching
mode, so reject any attempts to use it.
Signed-off-by: NMike Frysinger <vapier@gentoo.org>

arch/blackfin/mach-common/arch_checks.c

@@ -57,3 +57,8 @@
 	 (!defined(CONFIG_BFIN_EXTMEM_DCACHEABLE) && defined(CONFIG_BFIN_L2_WRITEBACK)))
 # error You are exposing Anomaly 220 in this config, either config L2 as Write Through, or make External Memory WB.
 #endif
+
+#if ANOMALY_05000475 && \
+	(defined(CONFIG_BFIN_EXTMEM_WRITEBACK) || defined(CONFIG_BFIN_L2_WRITEBACK))
+# error "Anomaly 475 does not allow you to use Write Back cache with L2 or External Memory"
+#endif