mtd: spi-nor: Use the spi_mem_xx() API

The spi_mem_xxx() API has been introduced to replace the
spi_flash_read() one. Make use of it so we can get rid of
spi_flash_read().

Note that using spi_mem_xx() also simplifies the code because this API
takes care of using the regular spi_sync() interface when the optimized
->mem_ops interface is not implemented by the controller.
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Frieder Schrempf <frieder.schrempf@exceet.de>
Tested-by: Frieder Schrempf <frieder.schrempf@exceet.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/mtd/devices/Kconfig

@@ -81,6 +81,7 @@ config MTD_DATAFLASH_OTP
 config MTD_M25P80
 	tristate "Support most SPI Flash chips (AT26DF, M25P, W25X, ...)"
 	depends on SPI_MASTER && MTD_SPI_NOR
+	select SPI_MEM
 	help
 	  This enables access to most modern SPI flash chips, used for
 	  program and data storage.   Series supported include Atmel AT26DF,