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/make_helpers/defaults.mk b/make_helpers/defaults.mk
index 8705d92..45f5fa8 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -96,6 +96,12 @@
 # Build option to enable MPAM for lower ELs
 ENABLE_MPAM_FOR_LOWER_ELS	:= 0
 
+# Enable the Maximum Power Mitigation Mechanism on supporting cores.
+ENABLE_MPMM			:= 0
+
+# Enable MPMM configuration via FCONF.
+ENABLE_MPMM_FCONF		:= 0
+
 # Flag to Enable Position Independant support (PIE)
 ENABLE_PIE			:= 0