spi: atmel-quadspi: Factor out switching to Serial Memory Mode to function

SAMA7G5 support (that was forward-ported from v6.1) re-introduced
a bug that was fixed in v6.12, thankfully only in the codepath of
the new SoC. But to prevent similar mistakes in the future, we
split out the offending code to a function, and use this, fixed
version everywhere.

To facilitate this, support function `atmel_qspi_update_config()`
also had to be moved upwards. For best viewing experience, use
`--color-moved-ws="allow-indentation-change" --color-moved`.

Fixes: 5af42209 ("spi: atmel-quadspi: Add support for sama7g5 QSPI")
Reported-by: Alexander Dahl <ada@thorsis.com>
Closes: https://lore.kernel.org/linux-spi/20241218-appliance-jaws-90773405977a@thorsis.com/


Signed-off-by: Bence Csókás <csokas.bence@prolan.hu>
Link: https://patch.msgid.link/20241218151754.365519-1-csokas.bence@prolan.hu


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