errata: workaround for Neoverse-V1 erratum 2108267

Neoverse-V1 erratum 2108267 is a Cat B erratum that applies to
revisions r0p0, r1p0, and r1p1 of CPU. It is still open. The
workaround is to write the value 2'b11 to the PF_MODE bits in
the CPUECTLR_EL1 register which will place the data prefetcher
in the most conservative mode instead of disabling it.

SDEN can be found here:
https://developer.arm.com/documentation/SDEN1401781/latest

Signed-off-by: nayanpatel-arm <nayankumar.patel@arm.com>
Change-Id: Iedcb84a7ad34af7083116818f49d7296f7d9bf94
diff --git a/docs/design/cpu-specific-build-macros.rst b/docs/design/cpu-specific-build-macros.rst
index 9676ae7..944228c 100644
--- a/docs/design/cpu-specific-build-macros.rst
+++ b/docs/design/cpu-specific-build-macros.rst
@@ -371,6 +371,10 @@
    CPU. This needs to be enabled for revisions r0p0, r1p0, and r1p1 of the
    CPU.  It is still open.
 
+-  ``ERRATA_V1_2108267``: This applies errata 2108267 workaround to Neoverse-V1
+   CPU. This needs to be enabled for revisions r0p0, r1p0, and r1p1 of the CPU.
+   It is still open.
+
 For Cortex-A710, the following errata build flags are defined :
 
 -  ``ERRATA_A710_1987031``: This applies errata 1987031 workaround to