spi: fsl-espi: eliminate spi nor flash read loop

The fsl-espi driver contains a read loop that implicitely assumes that
the device to read from is a m25p80 SPI NOR flash (bytes 2 - 4 of the
first write transfer are interpreted as 3 byte flash address).

Now that we have such a read loop in the spi-nor driver and are able
to correctly indicate the message size limit of the controller,
the read loop can be removed from the fsl-espi driver.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>