feat(fvp): enable FEAT_FGT by default

FEAT_FGT is one of the features for which Linux necessarily requires EL3
enablement, when the feature is present on a PE.

To cover the effect of different FVP command line parameters, include
the feature into the standard FVP build, but use FEAT_STATE_CHECK, to
always do runtime checks before accessing feature specific registers.

This prevents a Linux crash when the FVP is called with FEAT_FGT
enabled.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Change-Id: I55fbb2706aefbc3ab67c476e3f8b6ea74ae0d66c

plat/arm/board/fvp/platform.mk

@@ -463,6 +463,9 @@ ENABLE_SYS_REG_TRACE_FOR_NS	:= 1
 # enable trace filter control registers access to NS by default
 ENABLE_TRF_FOR_NS		:= 1
 
+# Linux relies on EL3 enablement if those features are present
+ENABLE_FEAT_FGT			:= 2
+
 ifeq (${SPMC_AT_EL3}, 1)
 PLAT_BL_COMMON_SOURCES	+=	plat/arm/board/fvp/fvp_el3_spmc.c
 endif