i2c_eeprom: Add reading support

This patch implements the reading functionality for the generic I2C
EEPROM driver, which was just a non-functional stub until now.

Since the page size will be of importance for the writing support, we
add suitable members to the private data structure to keep track of it.

Compatibility strings for a range of at24c* chips are added.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>

include/i2c_eeprom.h

@@ -14,6 +14,10 @@ struct i2c_eeprom_ops {
 };
 
 struct i2c_eeprom {
+	/* The EEPROM's page size in byte */
+	unsigned long pagesize;
+	/* The EEPROM's page width in bits (pagesize = 2^pagewidth) */
+	unsigned pagewidth;
 };
 
 #endif