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/Makefile b/Makefile
index 6f6d703..8c97b49 100644
--- a/Makefile
+++ b/Makefile
@@ -138,6 +138,10 @@
 
 include plat/${PLAT}/platform.mk
 
+# By default all CPU errata workarounds are disabled. This can be
+# overridden by the platform.
+include lib/cpus/cpu-errata.mk
+
 ifdef BL1_SOURCES
 NEED_BL1 := yes
 include bl1/bl1.mk