The spi-mem layer provides a spi_mem_supports_op() function to check
whether a specific operation is supported by the controller or not.
This is much more accurate than the hwcaps selection logic based on
SPI_{RX,TX}_ flags.

Rework the hwcaps selection logic to use spi_mem_supports_op() when
nor->spimem != NULL.
Signed-off-by: NBoris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: NVignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: NTudor Ambarus <tudor.ambarus@microchip.com>