fix(qemu-sbsa): fix compilation error when accessing DT functions

When building SBSA, using DT functions from fdt_wrappers.c produces a
linker error.  Adding:

BL2_SOURCES += ${FDT_WRAPPERS_SOURCES}

fixes the problem.  Since the same inclusion would be present in both
qemu/platform.mk and qemu_sbsa/platform.mk, do the changes in
qemu/common/common.mk.

Change-Id: I775b06c1741f6618813c5e1d2c64cdc1888d8519
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
diff --git a/plat/qemu/common/common.mk b/plat/qemu/common/common.mk
index ed95bc6..5f9f42b 100644
--- a/plat/qemu/common/common.mk
+++ b/plat/qemu/common/common.mk
@@ -65,7 +65,8 @@
 				${PLAT_QEMU_COMMON_PATH}/qemu_bl2_mem_params_desc.c	\
 				${PLAT_QEMU_COMMON_PATH}/qemu_image_load.c		\
 				common/desc_image_load.c		\
-				common/fdt_fixup.c
+				common/fdt_fixup.c			\
+				${FDT_WRAPPERS_SOURCES}
 
 BL31_SOURCES		+=	${QEMU_CPU_LIBS}				\
 				lib/semihosting/semihosting.c			\