i2c: i801: Call i2c_register_spd for muxed child segments

Once the gpio mux driver binds to the "i2c-mux-gpio" platform device,
this creates the i2c adapters for the muxed child segments.
We can use the bus notifier mechanism to check for creation of the
child i2c adapters, and call i2c_register_spd() for them. This allows
to detect all DIMM's on systems with more than 8 memory slots.

Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>