nand: zynq: Cleanup initialization

CONFIG_NAND_ZYNQ selects CONFIG_SYS_NAND_SELF_INIT, so the
driver doesn't have to play any ifdef game.

Also, we can mark zynq_nand_init() as static and get rid
of the mach-specific nand.h header.

This is really a revert of:
"mtd: zynq: nand: Move board_nand_init() function to board.c"
(sha1: 310995d9f91ae56082b49be06fe8c3d01424f8f6)

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Reviewed-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

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

@@ -1,9 +0,0 @@
-/*
- * 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

@@ -1006,7 +1006,7 @@ static int zynq_nand_device_ready(struct mtd_info *mtd)
 	return 0;
 }
 
-int zynq_nand_init(struct nand_chip *nand_chip, int devnum)
+static int zynq_nand_init(struct nand_chip *nand_chip, int devnum)
 {
 	struct zynq_nand_info *xnand;
 	struct mtd_info *mtd;
@@ -1192,14 +1192,12 @@ fail:
 	return err;
 }
 
-#ifdef CONFIG_SYS_NAND_SELF_INIT
 static struct nand_chip nand_chip[CONFIG_SYS_MAX_NAND_DEVICE];
 
-void __weak board_nand_init(void)
+void board_nand_init(void)
 {
 	struct nand_chip *nand = &nand_chip[0];
 
 	if (zynq_nand_init(nand, 0))
 		puts("ZYNQ NAND init failed\n");
 }
-#endif