spi: zynq_qspi: Add configuration to disable LQSPI feature

When the Zynq Boot ROM code loads the payload from QSPI it uses the
LQSPI feature of the QSPI device, however it does not clean up its
configuration before handing over to the payload which leaves the device
confgured to by-pass the standard non-linear operating mode.

This ensures the Linear QSPI mode is disabled before re-enabling the
device.

Signed-off-by: Nathan Rossi <nathan@nathanrossi.com>
Cc: Jagan Teki <jteki@openedev.com>
Cc: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>