build: Try to find fate_config.sh.template in source path

The FATE documentation depends on the mentioned file. But that
did break out of tree builds because the file was not found.

Signed-off-by: Alexander Strasser <eclipse7@gmx.net>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Makefile

@@ -8,6 +8,7 @@ vpath %.S    $(SRC_PATH)
 vpath %.asm  $(SRC_PATH)
 vpath %.v    $(SRC_PATH)
 vpath %.texi $(SRC_PATH)
+vpath %/fate_config.sh.template $(SRC_PATH)
 
 PROGS-$(CONFIG_FFMPEG)   += ffmpeg
 PROGS-$(CONFIG_AVCONV)   += avconv