Here's a patch for supporting the MX25U12835F part
Datasheet is here: http://www.macronix.com/Lists/DataSheet/Attachments/1653/MX25U12835F,%201.8V...
The ID was already in flashchips.h
1702 stefanct #define MACRONIX_MX25U12835E 0x2538 /* Same as MX25U12835F */
Martin