mtd: spi-nor: Changed spi-nor.c and spi.h for dual parallel support

Added dual parallel support for spi-nor

Signed-off-by: Anurag Kumar Vulisha <anuragku@xilinx.com>
Reviewed-by: Harini Katakam <harinik@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>