eeprom: 93xx46: extend driver to plug into the NVMEM framework

Add a regmap for accessing the EEPROM, and then use that with the
NVMEM framework. Enable backward compatibility in the NVMEM config
structure, so that the 'eeprom' file in sys is provided by the
framework.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>