spi: spi-ti-qspi: Support per spi-mem operation frequency switches

spi: spi-ti-qspi: Support per spi-mem operation frequency switches

Every ->exec_op() call correctly configures the spi bus speed to the
maximum allowed frequency for the memory using the constant spi default
parameter. Since we can now have per-operation constraints, let's use
the value that comes from the spi-mem operation structure instead. In
case there is no specific limitation for this operation, the default spi
device value will be given anyway.

The per-operation frequency capability is thus advertised to the spi-mem
core.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://patch.msgid.link/20241224-winbond-6-11-rc1-quad-support-v2-15-ad218dbc406f@bootlin.com
Signed-off-by: Mark Brown <broonie@kernel.org>