Add continuation ID support to jedec.c

Add continuation ID support to jedec.c
The continuation ID code does not go further than checking for IDs of
the type 0x7fXX, but does this for vendor and product ID. The current
published JEDEC spec has a list where the largest vendor ID is 7 bytes
long, but all leading bytes are 0x7f. The list will grow in the future,
and using a 64bit variable will not be enough anymore.
Besides that, it seems that the location of the ID byte after the first
continuation ID byte is very vendor specific, so we may have to revisit
that code some time in the future.

(Suggestion for a new encoding:
Use a two-byte data type for the ID, the lower byte contains the only
non-0x7f byte, the upper byte contains the number of 0x7f bytes used as
prefix, which is the bank number minus 1 the vendor ID appears in.)

Add support for EON EN29F002AT.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Acked-by: Corey Osgood <corey.osgood@gmail.com>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@3030 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1