feat(mpmm): add support for MPMM

MPMM - the Maximum Power Mitigation Mechanism - is an optional
microarchitectural feature present on some Armv9-A cores, introduced
with the Cortex-X2, Cortex-A710 and Cortex-A510 cores.

MPMM allows the SoC firmware to detect and limit high activity events
to assist in SoC processor power domain dynamic power budgeting and
limit the triggering of whole-rail (i.e. clock chopping) responses to
overcurrent conditions.

This feature is enabled via the `ENABLE_MPMM` build option.
Configuration can be done via FCONF by enabling `ENABLE_MPMM_FCONF`, or
by via the plaform-implemented `plat_mpmm_topology` function.

Change-Id: I77da82808ad4744ece8263f0bf215c5a091c3167
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/docs/getting_started/build-options.rst b/docs/getting_started/build-options.rst
index 8a0167b..da8d554 100644
--- a/docs/getting_started/build-options.rst
+++ b/docs/getting_started/build-options.rst
@@ -265,6 +265,16 @@
    partitioning in EL3, however. Platform initialisation code should configure
    and use partitions in EL3 as required. This option defaults to ``0``.
 
+-  ``ENABLE_MPMM``: Boolean option to enable support for the Maximum Power
+   Mitigation Mechanism supported by certain Arm cores, which allows the SoC
+   firmware to detect and limit high activity events to assist in SoC processor
+   power domain dynamic power budgeting and limit the triggering of whole-rail
+   (i.e. clock chopping) responses to overcurrent conditions. Defaults to ``0``.
+
+-  ``ENABLE_MPMM_FCONF``: Enables configuration of MPMM through FCONF, which
+   allows platforms with cores supporting MPMM to describe them via the
+   ``HW_CONFIG`` device tree blob. Default is 0.
+
 -  ``ENABLE_PIE``: Boolean option to enable Position Independent Executable(PIE)
    support within generic code in TF-A. This option is currently only supported
    in BL2_AT_EL3, BL31, and BL32 (TSP) for AARCH64 binaries, and in BL32