Add support for selected Cortex-A57 errata workarounds

This patch adds workarounds for selected errata which affect the Cortex-A57 r0p0
part. Each workaround has a build time flag which should be used by the platform
port to enable or disable the corresponding workaround. The workarounds are
disabled by default. An assertion is raised if the platform enables a workaround
which does not match the CPU revision at runtime.

Change-Id: I9ae96b01c6ff733d04dc733bd4e67dbf77b29fb0
diff --git a/include/lib/aarch64/arch.h b/include/lib/aarch64/arch.h
index 97242cc..b2aac2f 100644
--- a/include/lib/aarch64/arch.h
+++ b/include/lib/aarch64/arch.h
@@ -37,6 +37,8 @@
  ******************************************************************************/
 #define MIDR_IMPL_MASK		0xff
 #define MIDR_IMPL_SHIFT		0x18
+#define MIDR_VAR_SHIFT		20
+#define MIDR_REV_SHIFT		0
 #define MIDR_PN_MASK		0xfff
 #define MIDR_PN_SHIFT		0x4