fix(cpus): workaround for Cortex-X3 erratum 2266875

Cortex-X3 erratum 2266875 is a Cat B erratum that applies to
all revisions <= r1p0 and is fixed in r1p1. The workaround is to
set CPUACTLR_EL1[22]=1 which will cause the CFP instruction to
invalidate all branch predictor resources regardless of context.

SDEN Documentation:
https://developer.arm.com/documentation/2055130/latest

Change-Id: I9c610777e222f57f520d223bb03fc5ad05af1077
Signed-off-by: Bipin Ravi <bipin.ravi@arm.com>
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index 3a75dbd..287d32b 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -771,6 +771,10 @@
   CPU. This needs to be enabled only for revisions r0p0, r1p0, r1p1 and r1p2 of
   the CPU and is still open.
 
+- ``ERRATA_X3_2266875``: This applies errata 2266875 workaround to the Cortex-X3
+  CPU. This needs to be enabled only for revisions r0p0 and r1p0 of the CPU, it
+  is fixed in r1p1.
+
 - ``ERRATA_X3_2302506``: This applies errata 2302506 workaround to the Cortex-X3
   CPU. This needs to be enabled only for revisions r0p0, r1p0 and r1p1, it is
   fixed in r1p2.