libril: Use a board flag for video call field

xmm7260 on SLTE doesn't have this flag anymore. Devices which need it
should specify the flag.

Change-Id: I166f579274667919756d3bb90e0b182165525975
Signed-off-by: Andreas Schneider <asn@cryptomilk.org>

ril/libril/Android.mk

@@ -32,7 +32,7 @@ ifneq ($(filter m7450 mdm9x35 ss333 xmm7260,$(BOARD_MODEM_TYPE)),)
 LOCAL_CFLAGS := -DSAMSUNG_NEXT_GEN_MODEM
 endif
 
-ifneq ($(filter m7450 xmm7260,$(BOARD_MODEM_TYPE)),)
+ifeq ($(BOARD_MODEM_NEEDS_VIDEO_CALL_FIELD), true)
 LOCAL_CFLAGS += -DNEEDS_VIDEO_CALL_FIELD
 endif