spi: spi-mem: Allow specifying the byte order in Octal DTR mode

spi: spi-mem: Allow specifying the byte order in Octal DTR mode

There are NOR flashes (Macronix) that swap the bytes on a 16-bit
boundary when configured in Octal DTR mode. The byte order of
16-bit words is swapped when read or written in Octal Double
Transfer Rate (DTR) mode compared to Single Transfer Rate (STR)
modes. If one writes D0 D1 D2 D3 bytes using 1-1-1 mode, and uses
8D-8D-8D SPI mode for reading, it will read back D1 D0 D3 D2.
Swapping the bytes may introduce some endianness problems. It can
affect the boot sequence if the entire boot sequence is not handled
in either 8D-8D-8D mode or 1-1-1 mode. Therefore, it is necessary
to swap the bytes back to ensure the same byte order as in STR modes.
Fortunately there are controllers that could swap the bytes back at
runtime, addressing the flash's endianness requirements. Provide a
way for the upper layers to specify the byte order in Octal DTR mode.

Merge Tudor's patch and add modifications for suiting newer version
of Linux kernel.

Suggested-by: Michael Walle <mwalle@kernel.org>
Signed-off-by: JaimeLiao <jaimeliao@mxic.com.tw>
Signed-off-by: AlvinZhou <alvinzhou@mxic.com.tw>
Acked-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240926141956.2386374-3-alvinzhou.tw@gmail.com
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>