mtd: zynq: nand: Move board_nand_init() function to board.c

Putting board_nand_init() function inside NAND driver was not appropriate
due to it doesn't allow board vendor to customise their NAND
initialization code such as adding NAND lock/unlock code.

This commit was to move the board_nand_init() function from NAND driver
to board.c file. This allow customization of board_nand_init() function.

Signed-off-by: Wilson Lee <wilson.lee@ni.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Keng Soon Cheah <keng.soon.cheah@ni.com>
Cc: Chen Yee Chew <chen.yee.chew@ni.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Siva Durga Prasad Paladugu <siva.durga.paladugu@xilinx.com>
Cc: Scott Wood <oss@buserror.net>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/arm/mach-zynq/include/mach/nand.h

+/*
+ * Copyright (C) 2017 National Instruments Corp.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <nand.h>
+
+void zynq_nand_init(void);

drivers/mtd/nand/zynq_nand.c

@@ -994,7 +994,7 @@ static int zynq_nand_device_ready(struct mtd_info *mtd)
 	return 0;
 }
 
-static int zynq_nand_init(struct nand_chip *nand_chip, int devnum)
+int zynq_nand_init(struct nand_chip *nand_chip, int devnum)
 {
 	struct zynq_nand_info *xnand;
 	struct mtd_info *mtd;
@@ -1180,12 +1180,14 @@ fail:
 	return err;
 }
 
+#ifdef CONFIG_SYS_NAND_SELF_INIT
 static struct nand_chip nand_chip[CONFIG_SYS_MAX_NAND_DEVICE];
 
-void board_nand_init(void)
+void __weak board_nand_init(void)
 {
 	struct nand_chip *nand = &nand_chip[0];
 
 	if (zynq_nand_init(nand, 0))
 		puts("ZYNQ NAND init failed\n");
 }
+#endif