spi: xilinx_spi: Added support to read JEDEC-id twice at the boot time

This patch is for the startup block issue in the spi controller.
SPI clock is passing through STARTUP block to FLASH. STARTUP block
don't provide clock as soon as QSPI provides command. So, first
command fails.

This patch added support to read JEDEC id in xilinx_spi_xfer ().

Signed-off-by: Vipul Kumar <vipul.kumar@xilinx.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>