Add ARM errata workaround 852421 and 852423 for Cortex-A17

ARM errata 852421 and 852423 applies to r1p0, r1p1 and r1p2
revisions of Cortex-A17 processors. These workarounds
exist in Linux kernel and I thought it would be better
to add them in to U-Boot.

Signed-off-by: Nisal Menuka <nisalmenuka23@gmail.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 08480ac..054ccac 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -88,6 +88,12 @@
 config ARM_ERRATA_833471
 	bool
 
+config ARM_ERRATA_852421
+	bool
+
+config ARM_ERRATA_852423
+	bool
+
 config CPU_ARM720T
 	bool
 	select SYS_CACHE_SHIFT_5