cmd: eeprom: add support for layout aware commands

Introduce the (optional) eeprom print and eeprom update commands.

These commands are eeprom layout aware:
* The eeprom print command prints the contents of the eeprom in a human
  readable way (eeprom layout fields, and data formatted to be fit for human
  consumption).
* The eeprom update command allows user to update eeprom fields by specifying
  the field name, and providing the new data in a human readable format (same
  format as displayed by the eeprom print command).
* Both commands can either auto detect the layout, or be told which layout to
  use.

New CONFIG options:
CONFIG_CMD_EEPROM_LAYOUT - enables commands.
CONFIG_EEPROM_LAYOUT_HELP_STRING - tells user what layout names are supported

Feature API:
__weak int parse_layout_version(char *str)
	- override to provide your own layout name parsing
__weak void __eeprom_layout_assign(struct eeprom_layout *layout, int layout_version);
	- override to setup the layout metadata based on the version
__weak int eeprom_layout_detect(unsigned char *data)
	- override to provide your own algorithm for detecting layout version
eeprom_field.c
	- contains various printing and updating functions for common types of
	  eeprom fields. Can be used for defining custom layouts.

Cc: Heiko Schocher <hs@denx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Cc: Tom Rini <trini@konsulko.com>
Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>

include/eeprom_field.h

@@ -0,0 +1,39 @@
+/*
+ * (C) Copyright 2009-2016 CompuLab, Ltd.
+ *
+ * Authors: Nikita Kiryanov <nikita@compulab.co.il>
+ *	    Igor Grinberg <grinberg@compulab.co.il>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _FIELD_
+#define _FIELD_
+
+#define PRINT_FIELD_SEGMENT	"%-30s"
+
+struct eeprom_field {
+	char *name;
+	int size;
+	unsigned char *buf;
+
+	void (*print)(const struct eeprom_field *eeprom_field);
+	int (*update)(struct eeprom_field *eeprom_field, char *value);
+};
+
+void eeprom_field_print_bin(const struct eeprom_field *field);
+int eeprom_field_update_bin(struct eeprom_field *field, char *value);
+
+void eeprom_field_print_bin_rev(const struct eeprom_field *field);
+int eeprom_field_update_bin_rev(struct eeprom_field *field, char *value);
+
+void eeprom_field_print_mac(const struct eeprom_field *field);
+int eeprom_field_update_mac(struct eeprom_field *field, char *value);
+
+void eeprom_field_print_ascii(const struct eeprom_field *field);
+int eeprom_field_update_ascii(struct eeprom_field *field, char *value);
+
+void eeprom_field_print_reserved(const struct eeprom_field *field);
+int eeprom_field_update_reserved(struct eeprom_field *field, char *value);
+
+#endif