build(arm_fpga): add arm_fpga build

Adding PLAT=arm_fpga build to plat builds.

Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
Change-Id: Ia1573bf042a552637da21132f99a7f6221dc0572
diff --git a/tf_config/arm-fpga-default b/tf_config/arm-fpga-default
new file mode 100644
index 0000000..1264655
--- /dev/null
+++ b/tf_config/arm-fpga-default
@@ -0,0 +1,2 @@
+CROSS_COMPILE=aarch64-none-elf-
+PLAT=arm_fpga