feat(fvp): enable support for PSCI OS-initiated mode

Change-Id: I4cd6d2bd7ec7f581bd525d5323a3b54e855e2e51
Signed-off-by: Wing Li <wingers@google.com>
diff --git a/plat/arm/board/fvp/platform.mk b/plat/arm/board/fvp/platform.mk
index 207e0d7..143d10e 100644
--- a/plat/arm/board/fvp/platform.mk
+++ b/plat/arm/board/fvp/platform.mk
@@ -472,3 +472,5 @@
 ifeq (${SPMC_AT_EL3}, 1)
 PLAT_BL_COMMON_SOURCES	+=	plat/arm/board/fvp/fvp_el3_spmc.c
 endif
+
+PSCI_OS_INIT_MODE	:=	1