Added s25fs device

[ramonaerne]

Added s25fs device

This is almost identical to the s25fl devices with the following exceptions

• sector size is 256K not 64K
• subsector (4K) erase is only possible in the parameter section which is the low 32K or high 32K of the device
• some workaround is need in case a sector overlapping the parameter section is selected as we additionally need to erase the param section

To achieve this

• erase is overwritten and erases the param section before doing a sector erase that overlaps the param section
• can_erase is overwritten to check if an erase is requested in the param section otherwise only sector erases are allowed