zynq: treat ps7_init.c/h as external files to ignore them

ps7_init.c and ps7_init.h are supposed to be exported by hw project
and copied to board/xilinx/zynq/ directory.

We want them to be ignored by git.
So what we should do is to always treat them as external files
rather than replacing ps7_init.c

This commit does:

 - Move a weak function ps7_init() to arch/arm/cpu/armv7/zynq/spl.c
   and delete board/xilinx/zynq/ps7_init.c

 - Compile board/xilinx/zynq/ps7_init.c only when it exists

 - Add .gitignore to ignore ps7_init.c/h

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/arm/cpu/armv7/zynq/spl.c

@@ -74,3 +74,11 @@ int spl_start_uboot(void)
 	return 0;
 }
 #endif
+
+__weak void ps7_init(void)
+{
+	/*
+	 * This function is overridden by the one in
+	 * board/xilinx/zynq/ps7_init.c, if it exists.
+	 */
+}

board/xilinx/zynq/.gitignore

@@ -0,0 +1 @@
+ps7_init.[ch]

board/xilinx/zynq/Makefile

@@ -6,4 +6,7 @@
 #
 
 obj-y	:= board.o
-obj-$(CONFIG_SPL_BUILD)	+= ps7_init.o
+
+# Please copy ps7_init.c/h from hw project to this directory
+obj-$(CONFIG_SPL_BUILD) += \
+		$(if $(wildcard $(srctree)/$(src)/ps7_init.c), ps7_init.o)

board/xilinx/zynq/ps7_init.c

@@ -1,12 +0,0 @@
-/*
- * (C) Copyright 2014 Xilinx, Inc. Michal Simek
- *
- * SPDX-License-Identifier:    GPL-2.0+
- */
-#include <common.h>
-#include <asm/arch/spl.h>
-
-__weak void ps7_init(void)
-{
-	puts("Please copy ps7_init.c/h from hw project\n");
-}