Check presence of fix for errata 843419 in Cortex-A53

A fix for errata 843419 may be available in revision r0p4 of the
Cortex-A53 processor. The presence of the fix is determined by checking
bit 8 in the REVIDR register.

If the fix is present we report ERRATA_NOT_APPLIES which silences the
erroneous 'missing workaround' warning.

Change-Id: Ibd2a478df3e2a6325442a6a48a0bb0259dcfc1d7
Signed-off-by: Jonathan Wright <jonathan.wright@arm.com>
diff --git a/include/lib/cpus/aarch64/cpu_macros.S b/include/lib/cpus/aarch64/cpu_macros.S
index 8f0a74f..bfe2449 100644
--- a/include/lib/cpus/aarch64/cpu_macros.S
+++ b/include/lib/cpus/aarch64/cpu_macros.S
@@ -230,6 +230,7 @@
 
 	/* Check whether errata applies */
 	mov	x0, \_rev_var
+	/* Shall clobber: x0-x7 */
 	bl	check_errata_\_id
 
 	.ifeq \_chosen