stm32f2x: Increase options write timeout

stm32f2x: Increase options write timeout

Large flash parts time out when unlocking. Mass erase time is specified
as 32 seconds worst case for some parts. Automatic mass erase is
probably not using x8 parallelism, though, but a too large timeout
shouldn't hurt.

Also, use the new define instead of hardcoded timeout when mass
erasing.

Change-Id: Ib5af60d52ed7d53277bfe7176c4c44f79d3a26bc
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/3738
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>