radeonfb: fix chip definition for Radeon Xpress 200M 0x5975

This fixes a problem introduced with commit
b5f2f4d1
The commit added a wrong chip definition to radeonfb which causes
a blank console on my Laptop if radeonfb is loaded.

The patch
 - renames PCI_CHIP_RS485_5975 to PCI_CHIP_RS482_5975
 - corrects the chip family (RS480 instead of R300) for 0x5975
 - ensures that PCI IDs are in ascending order in ati_ids.h

Signed-off-by: Andreas Herrmann <aherrman@arcor.de>
Tentatively-acked-by: Ben Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>