Add support for reading SPD NVMEM data from SPD5118 (Jedec JESD300)
compliant memory modules. NVMEM write operation is not supported.

NVMEM support is optional. If CONFIG_NVMEM is disabled, the driver will
still instantiate but not provide NVMEM attribute files.
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Tested-by: Armin Wolf <W_Armin@gmx.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>