hwmon: (spd5118) Add support for reading SPD data

hwmon: (spd5118) Add support for reading SPD data

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>