linux-obmc: Unifiy defconfigs

Minimaise the differences between the ast2400 and ast2500 defconifgs.

ast2500 changes:
 - Enable IPv6
 - Disable unused compression algorithms
 - Enable SYN cookies
   * resolves https://github.com/openbmc/openbmc/issues/504
 - Enable kenrel hardening features
 - Disable unused USB support
 - Enable earlyprintk
 - Disable support for ancient libc

ast2400 changes:
 - Remove unused configfs support
 - Disable IPv6 IPSec support

Change-Id: Id1e388723160541de80b26c378b87a1a2da8091e
Signed-off-by: Joel Stanley <joel@jms.id.au>
2 files changed