PL2: Declare kernel image name

*Required for compilation

BoardConfig.mk

@@ -52,6 +52,7 @@ BOARD_KERNEL_PAGESIZE    := 4096
 BOARD_KERNEL_TAGS_OFFSET := 0x00000100
 BOARD_RAMDISK_OFFSET     := 0x01000000
 BOARD_SECOND_OFFSET      := 0x00f00000
+BOARD_KERNEL_IMAGE_NAME := Image.gz-dtb
 TARGET_PREBUILT_KERNEL := $(LOCAL_PATH)/prebuilt/Image.gz-dtb
 
 # Platform