mflash: Initial mflash support

Mflash is fusion memory device mainly targeted consumer eletronic and
mobile phone.
Internally, it have nand flash and other hardware logics and supports
some different operation (ATA, IO, XIP) modes.

IO mode is custom mode for the host that doesn't have IDE interface.
(Many mobile targeted SoC doesn't have IDE bus)

This driver support mflash IO mode.

Followings are brief descriptions about IO mode.

1. IO mode based on ATA protocol and uses some custom command. (read
   confirm, write confirm)
2. IO mode uses SRAM bus interface.

Signed-off-by: unsik Kim <donari75@gmail.com>

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diff --git a/doc/README.mflash b/doc/README.mflash
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+
+This document describes m[g]flash support in u-boot.
+
+Contents
+  1. Overview
+  2. Porting mflash driver
+  3. Mflash command
+  4. Misc.
+
+1. Overview
+Mflash and gflash are embedded flash drive. The only difference is mflash is
+MCP(Multi Chip Package) device. These two device operate exactly same way.
+So the rest mflash repersents mflash and gflash altogether.
+
+2. Porting mflash driver
+
+2-1. Board configuration
+* Mflash driver support
+#define CONFIG_CMD_MG_DISK
+#define CONFIG_LIBATA
+
+* Environment variable support (optional)
+#define CONFIG_ENV_IS_IN_MG_DISK
+Also CONFIG_ENV_ADDR and CONFIG_ENV_SIZE should be defined.
+CONFIG_ENV_ADDR is byte offset starting from 0.
+
+Following example sets environment variable location to 0x80000 (1024'th
+sector) and size of 0x400 (1024 byte)
+#define CONFIG_ENV_ADDR		0x80000
+#define CONFIG_ENV_SIZE		0x400
+
+* Reserved size config (optional)
+If you want to use some reserved area for bootloader, environment variable or
+whatever, use CONFIG_MG_DISK_RES. The unit is KB. Mflash's block operation
+method use this value as start offset. So any u-boot's partition table parser
+and file system command work consistently. You can access this area by using
+mflash command.
+
+Following example sets 10MB of reserved area.
+#define CONFIG_MG_DISK_RES	10240
+
+2-2. Porting mg_get_drv_data function
+Mflash is active device and need some gpio control for proper operation.
+This board dependency resolved by using mg_get_drv_data function.
+Port this function at your board init file. See include/mg_disk.h
+
+Here is some pseudo example.
+
+static void custom_hdrst_pin (u8 level)
+{
+	if (level)
+		/* set hard reset pin to high */
+	else
+		/* set hard reset pin to low */
+}
+
+static void custom_ctrl_pin_init (void)
+{
+	/* Set hard reset, write protect, deep power down pins
+	 * to gpio.
+	 * Set these pins to output high
+	 */
+}
+
+struct mg_drv_data* mg_get_drv_data (void)
+{
+	static struct mg_drv_data prv;
+
+	prv.base = /* base address of mflash */
+	prv.mg_ctrl_pin_init = custom_ctrl_pin_init;
+	prv.mg_hdrst_pin = custom_hdrst_pin;
+
+	return &prv;
+}
+
+3. Mflash command
+
+* initialize : mgd init
+* random read : mgd read [from] [to] [size]
+  ex) read 256 bytes from 0x300000 of mflash to 0xA0100000 of host memory
+      mgd read 0x300000 0xA0100000 256
+* random write : mgd write [from] [to] [size]
+* sector read : mgd readsec [sector] [to] [count]
+  ex) read 10 sectors starts from 400 sector to 0xA0100000
+      mgd readsec 400 0xA0100000 10
+* sector write : mgd writesec [from] [sector] [count]
+
+4. Misc.
+Mflash's device interface name for block driver is "mgd".
+Here is ext2 file system access example.
+
+ mgd init
+ ext2ls mgd 0:1 /boot
+ ext2load mgd 0:1 0xa0010000 /boot/uImage 1954156