imx: apalis_imx6: fix splash logo drawing

Define "splashimage" variable in the default environment
to enable splash screen drawing.

Signed-off-by: Anatolij Gustschin <agust@denx.de>

include/configs/apalis_imx6.h

@@ -213,6 +213,7 @@
 		"load ${interface} ${drive}:1 ${loadaddr} flash_blk.img && " \
 		"source ${loadaddr}\0" \
 	"splashpos=m,m\0" \
+	"splashimage=" __stringify(CONFIG_LOADADDR) "\0" \
 	"vidargs=mxc_hdmi.only_cea=1 " \
 		"video=mxcfb0:dev=hdmi,1920x1080M@60,if=RGB24 " \
 		"video=mxcfb1:off video=mxcfb2:off video=mxcfb3:off " \