fix(cpus): workaround for Cortex-A510 erratum 2666669

Cortex-A510 erratum 2666669 applies to revisions r1p1 and lower,
and is fixed in r1p2. The errata is mitigated by setting
IMP_CPUACTLR_EL1[38] to 1.

SDEN documentation:
https://developer.arm.com/documentation/SDEN1873351/latest
https://developer.arm.com/documentation/SDEN1873361/latest

Signed-off-by: Akram Ahmad <Akram.Ahmad@arm.com>
Change-Id: Ief27e4a155e43e75f05f2710d0c7bd5da2dec43f
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index f736e2d..721c399 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -616,6 +616,10 @@
    Cortex-A510 CPU. This needs to applied for revisions r0p0, r0p1, r0p2,
    r0p3, r1p0, r1p1, and is fixed in r1p2.
 
+-  ``ERRATA_A510_2666669``: This applies errata 2666669 workaround to
+   Cortex-A510 CPU. This needs to applied for revisions r0p0, r0p1, r0p2,
+   r0p3, r1p0, r1p1. It is fixed in r1p2.
+
 DSU Errata Workarounds
 ----------------------