stm32mp1: use newly introduced GICv2 makefile

Include the GICv2 makefile in STM32MP1 SP_min makefile, and use
${GICV2_SOURCES} instead of taking drivers/arm/gic files directly.

Change-Id: Ibcaed5b0bd17f6d8cf200e208c11cc10cd6d2ee5
Signed-off-by: Yann Gautier <yann.gautier@st.com>

plat/st/stm32mp1/sp_min/sp_min-stm32mp1.mk

@@ -16,9 +16,9 @@ BL32_SOURCES		+=	drivers/st/etzpc/etzpc.c			\
 				plat/st/stm32mp1/stm32mp1_topology.c
 
 # Generic GIC v2
-BL32_SOURCES		+=	drivers/arm/gic/common/gic_common.c	\
-				drivers/arm/gic/v2/gicv2_helpers.c	\
-				drivers/arm/gic/v2/gicv2_main.c		\
+include drivers/arm/gic/v2/gicv2.mk
+
+BL32_SOURCES		+=	${GICV2_SOURCES}			\
 				plat/common/plat_gicv2.c		\
 				plat/st/stm32mp1/stm32mp1_gic.c