Intel 82371EB: Add IDE init support.

Intel 82371EB: Add IDE init support.

In a mainboard's Config.lb file you can configure whether the primary
and/or secondary IDE interfaces shall be enabled.

Also, various fixups in the rest of the southbridge code, most notably
the early SMBus code, plus some documentation improvements.

Signed-off-by: Uwe Hermann <uwe@hermann-uwe.de>
Acked-by: Corey Osgood <corey_osgood@verizon.net>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@2703 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1