sf: spansion: Correct sector info for S25FL512S_256K

Corrected the pages_per_sector, nr_sectors info for
S25FL512S_256K flash which is added in below commit
"sf: spansion: Add support for S25FL512S_256K"
(sha1: b0f826bdae1b365970c4769247acbc5fb9b528e1)

Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
sf: spansion: Add support for S25FL256S_256K

Add support for Spansion S25FL256S_256K SPI flash.

Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>