spi: core: Add devm_spi_register_master()

Help simplify the cleanup code for SPI master drivers by providing a
managed master registration function, ensuring that the master is
automatically unregistered whenever the device is unbound.

Signed-off-by: Mark Brown <broonie@linaro.org>

diff --cc Documentation/driver-model/devres.txt
Simple merge

diff --cc drivers/spi/spi.c
Simple merge

diff --cc include/linux/spi/spi.h
Simple merge