spi: axi-spi-engine: use devm_spi_register_controller()

spi: axi-spi-engine: use devm_spi_register_controller()

This replaces spi_register_controller() with
devm_spi_register_controller() in the AXI SPI Engine driver. This
saves us from having to call spi_unregister_controller() in the
remove function.

The remove function is also removed since it is no longer needed.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20231117-axi-spi-engine-series-1-v1-7-cc59db999b87@baylibre.com
Signed-off-by: Mark Brown <broonie@kernel.org>