build(psci): move `runtime_errata.S` to PSCI

Move the runtime errata source file into the PSCI library, as PSCI is
the only component directly dependent on it, and it doesn't require
internal access to the CPUs library.

Change-Id: I92826714d49b1b0131f62c158543b4c167ab9aa8
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/lib/cpus/aarch64/runtime_errata.S b/lib/psci/aarch64/runtime_errata.S
similarity index 100%
rename from lib/cpus/aarch64/runtime_errata.S
rename to lib/psci/aarch64/runtime_errata.S
diff --git a/lib/psci/psci_lib.mk b/lib/psci/psci_lib.mk
index 6864202..c71580f 100644
--- a/lib/psci/psci_lib.mk
+++ b/lib/psci/psci_lib.mk
@@ -22,7 +22,7 @@
 
 ifeq (${ARCH}, aarch64)
 PSCI_LIB_SOURCES	+=	lib/el3_runtime/aarch64/context.S	\
-				lib/cpus/aarch64/runtime_errata.S
+				lib/psci/aarch64/runtime_errata.S
 endif
 
 ifeq (${USE_COHERENT_MEM}, 1)