spi: mxic: patch for octal DTR mode support

Driver patch for octal DTR mode support.

Owing to the spi_mem_default_supports_op() is not support dtr
operation. Based on commit <539cf68c

> (spi: spi-mem: add
spi_mem_dtr_supports_op()) add spi_mem_dtr_supports_op()
to support dtr and keep checking the buswidth and command bytes.

Signed-off-by: Zhengxun Li <zhengxunli@mxic.com.tw>
Link: https://lore.kernel.org/r/1628054827-458-1-git-send-email-zhengxunli@mxic.com.tw
Signed-off-by: Mark Brown <broonie@kernel.org>