spi: nxp_fspi: Ensure width is respected in spi-mem operations

Import linux commit 007773e16a6f ("spi: nxp-fspi: Ensure width is
respected in spi-mem operations") to fix SPI access on boards which
don't have all SPI I/O lines connected to the flash.

Since commit 71025f01 ("mtd: spi-nor-core: Rework hwcaps selection")
u-boot figures out the capabilities by looking at spi_mem_supports_op().
The FlexSPI driver doesn't take the board layout into account. Fix that.

Fixes: 383fded7 ("spi: nxp_fspi: new driver for the FlexSPI controller")
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>