spi: export of_find_spi_controller_by_node()

spi: export of_find_spi_controller_by_node()

Some devices are primarily described on another bus (e.g. I2C) but also
have an additional SPI connection that serves as a transport for
firmware loading. Export of_find_spi_controller_by_node() so drivers can
obtain the SPI controller referenced by a DT phandle.

Signed-off-by: Oder Chiou <oder_chiou@realtek.com>
Reviewed-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://patch.msgid.link/0e572a00aa305e588357162d400ba9472ce56dd3.1767148150.git.oder_chiou@realtek.com
Signed-off-by: Mark Brown <broonie@kernel.org>