A bit of googling suggests this is a GigaDevice GD25Q40. The most reliable source for that info probably being http://www.flashrom.org/pipermail/flashrom/2012-April/009060.html (Note that it's marked untested.)
A bit later it was renamed to GD25Q40(B), which is apparently the same thing. The manufacturer, which has a super-slow website (as far downloading data sheets goes), has a page for it http://www.gigadevice.com/product/detail/5/119.html
EDIT: In response to the question in the comment, there's a JEDEC standard (currently JEP106AP) doling out the flash mfg. numbers. GigaDevice has 8c assinged in there. Note that there are some "continuation bytes" now because they've ran out of mfg. ids in the original scheme. As for the device ID, I think they're (still) vendor-specific, i.e. it's up to the manufacturer to come up with them in way that doesn't cause incompatibilities/problems with their other chips. I'm not aware of a JEDEC (or other) centralized registry for device ids, except as it happens ad-hoc in flashing software. Some manufacturers make it easy to confirm the device id by putting it in their datasheet (e.g. Micron does that), but there's no device id in the aforementioned GigaDevice data sheet.