linux-imx

spi: Uninline spi_unregister_device()

Uninline spi_unregister_device() in preparation of adding more code to
it. Add kerneldoc documentation while we're at it.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@kernel.org>