i2c: i801: Simplify class-based client device instantiation

Now that the legacy eeprom driver was removed, the only remaining i2c
client driver with class SPD autodetection is jc42, and this driver
supports also class HWMON. Therefore we can remove class SPD from the
supported classes of the i801 adapter driver.
Legacy class-based instantiation shouldn't be used in new code, so I
think we can remove also the generic logic that ensures that supported
classes of parent and muxed adapters don't overlap.

Note: i801 parent supports just class HWMON now, and muxed childs
class SPD, so the supported classes don't overlap.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Acked-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>