sf: probe: Removed flag SECT_4K for Micron N25Q128

Remove the flag SECT_4K for device N25Q128 as the 4K-byte
sub sector erase granularity is available only for top/
bottom 8 sectors in some of the N25Q128 chips.

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