sf: Fix Bank selection calculation for Dual parallel

In Dual parallel connection the bank selection calculation
should be performed using offset and not the calculated address

Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
sf: Add support for Spansion S25FL128S_256K

Add support for Spansion device S25FL128S_256K

Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>