soc.mk: do not clobber TARGET_KERNEL_CONFIGS

This variable is a list of multiple kconf entries, so don't clobber it.

BUG=b/27675566
TEST=built edison w/custom settings and it works now

Change-Id: If6bdf872a6431b06c4cb5d1811db111a05d98995

soc/fs1130/soc.mk

@@ -46,7 +46,7 @@ BOARD_SEPOLICY_DIRS += \
 
 TARGET_KERNEL_SRC := hardware/bsp/kernel/imagination/v4.1
 TARGET_KERNEL_DEFCONFIG := pistachio_defconfig
-TARGET_KERNEL_CONFIGS := $(realpath $(LOCAL_PATH)/soc.kconf)
+TARGET_KERNEL_CONFIGS := $(TARGET_KERNEL_CONFIGS) $(realpath $(LOCAL_PATH)/soc.kconf)
 
 # Keystore HAL
 DEVICE_PACKAGES += \