mtd: nand: provide several helpers to do common NAND operations

This is part of the process of removing direct calls to ->cmdfunc()
outside of the core in order to introduce a better interface to execute
NAND operations.

Here we provide several helpers and make use of them to remove all
direct calls to ->cmdfunc(). This way, we can easily modify those
helpers to make use of the new ->exec_op() interface when available.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
[miquel.raynal@free-electrons.com: rebased and fixed some conflicts]
Signed-off-by: Miquel Raynal <miquel.raynal@free-electrons.com>
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/drivers/mtd/nand/diskonchip.c b/drivers/mtd/nand/diskonchip.c
index 72671dc..6bc93ea 100644
--- a/drivers/mtd/nand/diskonchip.c
+++ b/drivers/mtd/nand/diskonchip.c
@@ -448,7 +448,7 @@
 	int status;
 
 	DoC_WaitReady(doc);
-	this->cmdfunc(mtd, NAND_CMD_STATUS, -1, -1);
+	nand_status_op(this, NULL);
 	DoC_WaitReady(doc);
 	status = (int)this->read_byte(mtd);
 
@@ -595,7 +595,7 @@
 
 	/* Assert ChipEnable and deassert WriteProtect */
 	WriteDOC((DOC_FLASH_CE), docptr, Mplus_FlashSelect);
-	this->cmdfunc(mtd, NAND_CMD_RESET, -1, -1);
+	nand_reset_op(this);
 
 	doc->curchip = chip;
 	doc->curfloor = floor;