spi: spi-axi-spi-engine: Add support for MOSI idle configuration

Implement MOSI idle low and MOSI idle high to better support peripherals
that request specific MOSI behavior.

Acked-by: Nuno Sa <nuno.sa@analog.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Link: https://patch.msgid.link/f237166c7bbe0a1cdabce243b97484bf2f428143.1720810545.git.marcelo.schmitt@analog.com


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