Fix ATMEL 29C020 detection with flashrom. The JEDEC probe routine had

Fix ATMEL 29C020 detection with flashrom. The JEDEC probe routine had
a delay of 10 us after entering ID mode and this was insufficient for
the 29C020. The data sheet claims we have to wait 10 ms, but tests have
shown that 20 us suffice. Allow for variations in chip delays with a
factor of 2 safety margin.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Acked-by: Peter Stuge <peter@stuge.se>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@2962 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1