spi: spidev: Restore loading from Device Tree

As happens occasionally, an upstream change has once again prevented
spidev from being loaded via Device Tree. We now need "spidev" to be
included in the new spi_device_id list, otherwise although the
spidev driver gets loaded no /dev/spidev*.* entries will appear.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>