sf: Default page size Spansion flash "S25FS512S" is 256b

page size for JEDEC EXT starting 0x4d00 is 512b,
except JEDEC ID 0x215, 0x216 and 0x220

Signed-off-by: Ashish Kumar <Ashish.Kumar@nxp.com>
[jagan: added proper commit message]
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>