fix(fvp): enable FEAT_MTE2

ENABLE_FEAT_MTE2 controls the trapping of some MTE related system
registers. If the memory_tagging_support_level parameter on the FVP
command line is set to higher values, non-secure world will see the
feature bits in the CPU ID registers and will use those registers,
triggering a panic in BL31.

Enable the feature in the optional form for the FVP build, to avoid any
panics.

Change-Id: I26ba444d784adf165db81048f93e11361c7f11ac
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/plat/arm/board/fvp/platform.mk b/plat/arm/board/fvp/platform.mk
index 340eb38..bbd9141 100644
--- a/plat/arm/board/fvp/platform.mk
+++ b/plat/arm/board/fvp/platform.mk
@@ -76,6 +76,7 @@
 ENABLE_FEAT_S1PIE		:= 2
 ENABLE_FEAT_S2POE		:= 2
 ENABLE_FEAT_S1POE		:= 2
+ENABLE_FEAT_MTE2		:= 2
 
 # The FVP platform depends on this macro to build with correct GIC driver.
 $(eval $(call add_define,FVP_USE_GIC_DRIVER))